[HACK] libstdc++: Force atomic builtin checks to use sparc v8

This in effect forces libstdc++ to refuse to use the atomic builtins
unless they're going to work across a more sensible range of CPU
configurations.  Without this hack libstdc++ detects that they're
present with the default cpu (presumably v9, even 32bit) and instead
fails at link-time for non-v9 code.

libstdc++-v3/acinclude.m4

@@ -2444,7 +2444,11 @@ AC_DEFUN([GLIBCXX_ENABLE_ATOMIC_BUILTINS], [
   old_CXXFLAGS="$CXXFLAGS"
   
   # Compile unoptimized.
-  CXXFLAGS='-O0 -S'
+  # XXX: On sparc, use the lowest practical CPU level # to avoid false positives
+  case $host in
+      sparc*-*solaris*) CXXFLAGGS='-O0 -S -mcpu=v8';;
+      *) CXXFLAGS='-O0 -S';;
+  esac
 
   # Fake what AC_TRY_COMPILE does, without linking as this is
   # unnecessary for a builtins test.

libstdc++-v3/configure

@@ -14758,7 +14758,11 @@ ac_compiler_gnu=$ac_cv_cxx_compiler_gnu
   old_CXXFLAGS="$CXXFLAGS"
 
   # Compile unoptimized.
-  CXXFLAGS='-O0 -S'
+  # XXX: On sparc, use the lowest practical CPU level # to avoid false positives
+  case $host in
+      sparc*-*solaris*) CXXFLAGS='-O0 -S -mcpu=v8';;
+      *) CXXFLAGS='-O0 -S';;
+  esac
 
   # Fake what AC_TRY_COMPILE does, without linking as this is
   # unnecessary for a builtins test.