[msvc] Ignore some warnings on msvc

Port a partial revert of https://crrev.com/c/3189512. The comments are
kept around to document what each flag does.

Fixed: chromium:1255096
Change-Id: I8758a536a6f77826b0eb4918d7d8c85b772d9394
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3203004
Reviewed-by: Shu-yu Guo <syg@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77227}

BUILD.gn

@@ -1254,7 +1254,144 @@ config("toolchain") {
   }
 
   if (!is_clang && is_win) {
-    cflags += [ "/wd4506" ]  # Benign "no definition for inline function"
+    cflags += [
+      "/wd4506",  # Benign "no definition for inline function"
+
+      # Warnings permanently disabled:
+
+      # C4091: 'typedef ': ignored on left of 'X' when no variable is
+      #                    declared.
+      # This happens in a number of Windows headers. Dumb.
+      "/wd4091",
+
+      # C4127: conditional expression is constant
+      # This warning can in theory catch dead code and other problems, but
+      # triggers in far too many desirable cases where the conditional
+      # expression is either set by macros or corresponds some legitimate
+      # compile-time constant expression (due to constant template args,
+      # conditionals comparing the sizes of different types, etc.).  Some of
+      # these can be worked around, but it's not worth it.
+      "/wd4127",
+
+      # C4251: 'identifier' : class 'type' needs to have dll-interface to be
+      #        used by clients of class 'type2'
+      # This is necessary for the shared library build.
+      "/wd4251",
+
+      # C4275:  non dll-interface class used as base for dll-interface class
+      # This points out a potential (but rare) problem with referencing static
+      # fields of a non-exported base, through the base's non-exported inline
+      # functions, or directly. The warning is subtle enough that people just
+      # suppressed it when they saw it, so it's not worth it.
+      "/wd4275",
+
+      # C4312 is a VS 2015 64-bit warning for integer to larger pointer.
+      # TODO(brucedawson): fix warnings, crbug.com/554200
+      "/wd4312",
+
+      # C4324 warns when padding is added to fulfill alignas requirements,
+      # but can trigger in benign cases that are difficult to individually
+      # suppress.
+      "/wd4324",
+
+      # C4351: new behavior: elements of array 'array' will be default
+      #        initialized
+      # This is a silly "warning" that basically just alerts you that the
+      # compiler is going to actually follow the language spec like it's
+      # supposed to, instead of not following it like old buggy versions did.
+      # There's absolutely no reason to turn this on.
+      "/wd4351",
+
+      # C4355: 'this': used in base member initializer list
+      # It's commonly useful to pass |this| to objects in a class' initializer
+      # list.  While this warning can catch real bugs, most of the time the
+      # constructors in question don't attempt to call methods on the passed-in
+      # pointer (until later), and annotating every legit usage of this is
+      # simply more hassle than the warning is worth.
+      "/wd4355",
+
+      # C4503: 'identifier': decorated name length exceeded, name was
+      #        truncated
+      # This only means that some long error messages might have truncated
+      # identifiers in the presence of lots of templates.  It has no effect on
+      # program correctness and there's no real reason to waste time trying to
+      # prevent it.
+      "/wd4503",
+
+      # Warning C4589 says: "Constructor of abstract class ignores
+      # initializer for virtual base class." Disable this warning because it
+      # is flaky in VS 2015 RTM. It triggers on compiler generated
+      # copy-constructors in some cases.
+      "/wd4589",
+
+      # C4611: interaction between 'function' and C++ object destruction is
+      #        non-portable
+      # This warning is unavoidable when using e.g. setjmp/longjmp.  MSDN
+      # suggests using exceptions instead of setjmp/longjmp for C++, but
+      # Chromium code compiles without exception support.  We therefore have to
+      # use setjmp/longjmp for e.g. JPEG decode error handling, which means we
+      # have to turn off this warning (and be careful about how object
+      # destruction happens in such cases).
+      "/wd4611",
+
+      # Warnings to evaluate and possibly fix/reenable later:
+
+      "/wd4100",  # Unreferenced formal function parameter.
+      "/wd4121",  # Alignment of a member was sensitive to packing.
+      "/wd4244",  # Conversion: possible loss of data.
+      "/wd4505",  # Unreferenced local function has been removed.
+      "/wd4510",  # Default constructor could not be generated.
+      "/wd4512",  # Assignment operator could not be generated.
+      "/wd4610",  # Class can never be instantiated, constructor required.
+      "/wd4838",  # Narrowing conversion. Doesn't seem to be very useful.
+      "/wd4995",  # 'X': name was marked as #pragma deprecated
+      "/wd4996",  # Deprecated function warning.
+
+      # These are variable shadowing warnings that are new in VS2015. We
+      # should work through these at some point -- they may be removed from
+      # the RTM release in the /W4 set.
+      "/wd4456",
+      "/wd4457",
+      "/wd4458",
+      "/wd4459",
+
+      # All of our compilers support the extensions below.
+      "/wd4200",  # nonstandard extension used: zero-sized array in struct/union
+      "/wd4201",  # nonstandard extension used: nameless struct/union
+      "/wd4204",  # nonstandard extension used : non-constant aggregate
+                  # initializer
+
+      "/wd4221",  # nonstandard extension used : 'identifier' : cannot be
+                  # initialized using address of automatic variable
+
+      # http://crbug.com/588506 - Conversion suppressions waiting on Clang
+      # -Wconversion.
+      "/wd4245",  # 'conversion' : conversion from 'type1' to 'type2',
+                  # signed/unsigned mismatch
+
+      "/wd4267",  # 'var' : conversion from 'size_t' to 'type', possible loss of
+                  # data
+
+      "/wd4305",  # 'identifier' : truncation from 'type1' to 'type2'
+      "/wd4389",  # 'operator' : signed/unsigned mismatch
+
+      "/wd4702",  # unreachable code
+
+      # http://crbug.com/848979 - MSVC is more conservative than Clang with
+      # regards to variables initialized and consumed in different branches.
+      "/wd4701",  # Potentially uninitialized local variable 'name' used
+      "/wd4703",  # Potentially uninitialized local pointer variable 'name' used
+
+      # http://crbug.com/848979 - Remaining Clang permitted warnings.
+      "/wd4661",  # 'identifier' : no suitable definition provided for explicit
+                  # template instantiation request
+
+      "/wd4706",  # assignment within conditional expression
+                  # MSVC is stricter and requires a boolean expression.
+
+      "/wd4715",  # 'function' : not all control paths return a value'
+                  # MSVC does not analyze switch (enum) for completeness.
+    ]
   }
 
   if (!is_clang && !is_win) {