Bug 1397263 - move GNU_AS checks to toolchain.configure; r=glandium

The GNU_AS check in old-configure depended on running with the value
of $AS before it gets reset to just be the C compiler, which breaks when
we move setting AS into moz.configure.

This patch moves the GNU_AS check to toolchain.configure and changes it
so that it works when the assembler is the C compiler.  We do have to
fix things slightly for clang, because the previous check was
succeeding, but not because of clang: it was detecting the presence of
"GNU" in the output for GNU ld/gold and a message about the GNU GPL.

build/autoconf/toolchain.m4

@@ -14,8 +14,6 @@ define([AC_HEADER_STDC], [])
 
 AC_DEFUN([MOZ_TOOL_VARIABLES],
 [
-GNU_AS=
-
 GNU_CC=
 GNU_CXX=
 if test "$CC_TYPE" = "gcc"; then
@@ -23,11 +21,6 @@ if test "$CC_TYPE" = "gcc"; then
     GNU_CXX=1
 fi
 
-if test "`echo | $AS -o conftest.out -v 2>&1 | grep -c GNU`" != "0"; then
-    GNU_AS=1
-fi
-rm -f conftest.out
-
 CLANG_CC=
 CLANG_CXX=
 CLANG_CL=

build/moz.configure/toolchain.configure

@@ -1869,6 +1869,32 @@ def as_with_flags(as_info, assembler, provided_assembler, c_compiler):
 
 add_old_configure_assignment('AS', as_with_flags)
 
+
+@depends(assembler, c_compiler, extra_toolchain_flags)
+@imports('subprocess')
+@imports(_from='os', _import='devnull')
+def gnu_as(assembler, c_compiler, toolchain_flags):
+    # clang uses a compatible GNU assembler.
+    if c_compiler.type == 'clang':
+        return True
+
+    if c_compiler.type == 'gcc':
+        cmd = [assembler] + c_compiler.flags
+        if toolchain_flags:
+            cmd += toolchain_flags
+        cmd += ['-Wa,--version', '-c', '-o', devnull, '-x', 'assembler', '-']
+        # We don't actually have to provide any input on stdin, `Popen.communicate` will
+        # close the stdin pipe.
+        # clang will error if it uses its integrated assembler for this target,
+        # so handle failures gracefully.
+        if 'GNU' in check_cmd_output(*cmd, stdin=subprocess.PIPE, onerror=lambda: '').decode('utf-8'):
+            return True
+
+
+set_config('GNU_AS', gnu_as)
+add_old_configure_assignment('GNU_AS', gnu_as)
+
+
 @depends(as_info, target)
 def as_dash_c_flag(as_info, target):
     # armasm64 doesn't understand -c.

js/src/old-configure.in

@@ -302,7 +302,6 @@ AC_SUBST(QEMU_CANT_RUN_JS_SHELL)
 
 AC_SUBST(_MSC_VER)
 
-AC_SUBST(GNU_AS)
 AC_SUBST(GNU_CC)
 AC_SUBST(GNU_CXX)
 

old-configure.in

@@ -333,7 +333,6 @@ fi # COMPILE_ENVIRONMENT
 
 AC_SUBST(_MSC_VER)
 
-AC_SUBST(GNU_AS)
 AC_SUBST(GNU_CC)
 AC_SUBST(GNU_CXX)