hurd: Fix ld.so link

Since a2e8aa0d9e ("Block signals during the initial part of dlopen") dl_open
uses sigprocmask, so we need a stub implementation.

sysdeps/mach/hurd/Versions

@@ -1,7 +1,7 @@
 libc {
   GLIBC_2.0 {
     # functions with a weak definition in the dynamic linker
-    __access; __getcwd; __mmap;
+    __access; __getcwd; __mmap; __sigprocmask;
   }
   GLIBC_2.2.6 {
     # functions with a weak definition in the dynamic linker
@@ -26,7 +26,7 @@ ld {
     __mmap; __open; __read; __sbrk; __strtoul_internal;
     __write; __writev; __xstat64; __fxstat64;
     _exit; _hurd_intr_rpc_mach_msg;
-    abort;
+    abort; __sigprocmask;
   }
   GLIBC_2.2 {
     # functions that must be shared with libc

sysdeps/mach/hurd/dl-sysdep.c

@@ -264,13 +264,14 @@ _dl_sysdep_start_cleanup (void)
   __mach_port_deallocate (__mach_task_self (), __mach_task_self_);
 }
 
-/* Minimal open/close/mmap implementation sufficient for initial loading of
+/* Minimal open/close/mmap/etc. implementation sufficient for initial loading of
    shared libraries.  These are weak definitions so that when the
    dynamic linker re-relocates itself to be user-visible (for -ldl),
    it will get the user's definition (i.e. usually libc's).
 
-   They also need to be set in the ld section of sysdeps/mach/hurd/Versions, to
-   be overridable, and in libc.abilist and ld.abilist to be checked. */
+   They also need to be set in the libc and ld section of
+   sysdeps/mach/hurd/Versions, to be overridable, and in libc.abilist and
+   ld.abilist to be checked. */
 
 /* This macro checks that the function does not get renamed to be hidden: we do
    need these to be overridable by libc's.  */
@@ -674,6 +675,14 @@ strong_alias (abort, __GI___chk_fail)
 strong_alias (abort, __GI___fortify_fail)
 strong_alias (abort, __GI___assert_fail)
 strong_alias (abort, __GI___assert_perror_fail)
+
+check_no_hidden(__sigprocmask);
+int weak_function
+__sigprocmask (int how, const sigset_t *set, sigset_t *oset)
+{
+  /* We do not have signals yet at this stage.  */
+  return 0;
+}
 
 /* This function is called by interruptible RPC stubs.  For initial
    dynamic linking, just use the normal mach_msg.  Since this defn is

sysdeps/mach/hurd/i386/ld.abilist

@@ -8,6 +8,7 @@ GLIBC_2.2.6 __open F
 GLIBC_2.2.6 __open64 F
 GLIBC_2.2.6 __read F
 GLIBC_2.2.6 __sbrk F
+GLIBC_2.2.6 __sigprocmask F
 GLIBC_2.2.6 __strtoul_internal F
 GLIBC_2.2.6 __write F
 GLIBC_2.2.6 __writev F

sysdeps/mach/hurd/i386/libc.abilist

@@ -426,6 +426,7 @@ GLIBC_2.2.6 __signbit F
 GLIBC_2.2.6 __signbitf F
 GLIBC_2.2.6 __signbitl F
 GLIBC_2.2.6 __sigpause F
+GLIBC_2.2.6 __sigprocmask F
 GLIBC_2.2.6 __sigsetjmp F
 GLIBC_2.2.6 __sigsuspend F
 GLIBC_2.2.6 __stpcpy F

sysdeps/mach/hurd/i386/localplt.data

@@ -40,6 +40,7 @@ ld.so: __sbrk
 ld.so: __strtoul_internal
 #ld.so: _exit
 ld.so: abort
+ld.so: __sigprocmask
 ld.so: _hurd_intr_rpc_mach_msg
 ld.so: __errno_location
 # rtld_hidden is currently disabled to avoid having to special-case the