Updates to QA scrdiff script to keep package configure macros in sync.

m4/visibility_hidden.m4

@@ -0,0 +1,22 @@
+AC_DEFUN([AC_FUNC_GCC_VISIBILITY],
+  [AC_CACHE_CHECK(whether __attribute__((visibility())) is supported,
+		  libc_cv_visibility_attribute,
+		  [cat > conftest.c <<EOF
+		   int foo __attribute__ ((visibility ("hidden"))) = 1;
+		   int bar __attribute__ ((visibility ("protected"))) = 1;
+EOF
+		  libc_cv_visibility_attribute=no
+		  if ${CC-cc} -Werror -S conftest.c -o conftest.s \
+			>/dev/null 2>&1; then
+		    if grep '\.hidden.*foo' conftest.s >/dev/null; then
+		      if grep '\.protected.*bar' conftest.s >/dev/null; then
+			libc_cv_visibility_attribute=yes
+		      fi
+		    fi
+		  fi
+		  rm -f conftest.[cs]
+		  ])
+   if test $libc_cv_visibility_attribute = yes; then
+     AC_DEFINE(HAVE_VISIBILITY_ATTRIBUTE)
+   fi
+  ])