configure: Enable gas-preprocessor on all OSes but only if available

Signed-off-by: Martin Storsjö <martin@martin.st>

configure

@@ -2199,8 +2199,6 @@ ranlib="ranlib"
 strip="strip"
 yasmexe="yasm"
 
-nogas=":"
-
 # machine
 arch_default=$(uname -m)
 cpu="generic"
@@ -3424,7 +3422,6 @@ case $target_os in
         add_extralibs -lpoll -lgnugetopt
         ;;
     darwin)
-        gas="gas-preprocessor.pl $cc"
         enabled ppc && add_asflags -force_cpusubtype_ALL
         SHFLAGS='-dynamiclib -Wl,-single_module -Wl,-install_name,$(SHLIBDIR)/$(SLIBNAME_WITH_MAJOR),-current_version,$(LIBVERSION),-compatibility_version,$(LIBMAJOR)'
         enabled x86_32 && append SHFLAGS -Wl,-read_only_relocs,suppress
@@ -3783,8 +3780,21 @@ EOF
 }
 
 if enabled_any arm aarch64 || enabled_all ppc altivec && enabled asm; then
+    nogas=:
     enabled_any arm aarch64 && nogas=die
     enabled_all ppc altivec && nogas=warn
+    as_noop=-v
+
+    case $as_type in
+        arm*) gaspp_as_type=armasm; as_noop=-h ;;
+        gcc)  gaspp_as_type=gas ;;
+        *)    gaspp_as_type=$as_type ;;
+    esac
+
+    [ $target_os = "darwin" ] && gaspp_as_type="apple-$gaspp_as_type"
+
+    check_cmd gas-preprocessor.pl -arch $arch -as-type $gaspp_as_type -- $as $as_noop &&
+        gas="gas-preprocessor.pl -arch $arch -as-type $gaspp_as_type -- $as"
 
     if ! check_gas ; then
         as=${gas:=$as}