Disable _TIME_BITS if the compiler defaults to it

Even though building glibc with 64 bit time_t flags is not supported,
and the usual way is to patch the build system to avoid it; some
systems do enable it by default, and it increases the requirements
to build glibc in such cases (it also does not help newcomers when
trying to build glibc).

The conform namespace and linknamespace tests also do not expect
that flag to be set by default, so disable it as well.

Checked with a build/check for major ABI and some (i386, arm,
mipsel, hppa) with a toolchain that has LFS flags by default.
Reviewed-by: DJ Delorie <dj@redhat.com>

Makeconfig

@@ -1014,6 +1014,9 @@ endif
 # Filter out LFS flags if compiler defines it by default.
 +cflags += $(no-file-offset-bits-source)
 
+# Filter out 64 bit time_t flags if compiler defines it by default.
++cflags += $(no-time-bits-source)
+
 # Each sysdeps directory can contain header files that both will be
 # used to compile and will be installed.  Each can also contain an
 # include/ subdirectory, whose header files will be used to compile

configure

@@ -635,6 +635,7 @@ libc_cv_gcc_unwind_find_fde
 libc_extra_cppflags
 libc_extra_cflags
 libc_cv_cxx_thread_local
+no_time_bits_source
 no_file_offset_bits_source
 fortify_source
 no_fortify_source
@@ -7815,6 +7816,35 @@ fi
 config_vars="$config_vars
 no-file-offset-bits-source = $no_file_offset_bits_source"
 
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+int
+main (void)
+{
+
+#ifndef _TIME_BITS
+# error _TIME_BITS not defined
+#endif
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_cpp "$LINENO"
+then :
+  libc_cv_compiler_default_time_bits=yes
+else case e in #(
+  e) libc_cv_compiler_default_time_bits=no ;;
+esac
+fi
+rm -f conftest.err conftest.i conftest.$ac_ext
+if test "$libc_cv_compiler_default_time_bits" = yes
+then :
+  no_time_bits_source="-U_TIME_BITS"
+fi
+
+config_vars="$config_vars
+no-time-bits-source = $no_time_bits_source"
 
 { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether the assembler requires one version per symbol" >&5
 printf %s "checking whether the assembler requires one version per symbol... " >&6; }

configure.ac

@@ -1576,6 +1576,17 @@ AS_IF([test "$libc_cv_compiler_default_file_offset_bits" = yes],
 AC_SUBST(no_file_offset_bits_source)
 LIBC_CONFIG_VAR([no-file-offset-bits-source], [$no_file_offset_bits_source])
 
+dnl Check if compiler define _TIME_BITS by default
+AC_PREPROC_IFELSE([AC_LANG_PROGRAM([[]], [[
+#ifndef _TIME_BITS
+# error _TIME_BITS not defined
+#endif]])],
+	       [libc_cv_compiler_default_time_bits=yes],
+	       [libc_cv_compiler_default_time_bits=no])
+AS_IF([test "$libc_cv_compiler_default_time_bits" = yes],
+      [no_time_bits_source="-U_TIME_BITS"])
+AC_SUBST(no_time_bits_source)
+LIBC_CONFIG_VAR([no-time-bits-source], [$no_time_bits_source])
 
 dnl Starting with binutils 2.35, GAS can attach multiple symbol versions
 dnl to one symbol (PR 23840).

conform/Makefile

@@ -372,7 +372,7 @@ test-xfail-UNIX98/ndbm.h/conform = yes
 test-xfail-XOPEN2K/ndbm.h/conform = yes
 test-xfail-XOPEN2K8/ndbm.h/conform = yes
 
-conformtest-cc-flags =  -I../include $(+sysdep-includes) $(sysincludes) -I.. $(no-file-offset-bits-source)
+conformtest-cc-flags =  -I../include $(+sysdep-includes) $(sysincludes) -I.. $(no-file-offset-bits-source) $(no-time-bits-source)
 # conformtest-xfail-conds may be set by a sysdeps Makefile fragment to
 # a list of conditions that are considered to be true when encountered
 # in xfail[cond]- lines in test expectations.