testsuite: Detect clang

Clang doesn't like the -Wno-psabi argument that we want to pass to GCC.
Since clang is detected as GCC via __GNUC__, use ax_cv_c_compiler_vendor.

testsuite/lib/libffi.exp

@@ -100,18 +100,16 @@ proc libffi-init { args } {
     global libffi_link_flags
     global tool_root_dir
     global ld_library_path
-
+    global compiler_vendor
-    global using_gcc
 
     set blddirffi [pwd]/.. 
     verbose "libffi $blddirffi"
 
-    # Are we building with GCC?
+    # Which compiler are we building with?
-    set tmp [grep ../config.status "GCC='yes'"]
+    set tmp [grep ../config.log "^ax_cv_c_compiler_vendor.*$"]
-    if { [string match $tmp "GCC='yes'"] } {
+    regexp -- {^[^=]*=(.*)$} $tmp nil compiler_vendor
-
-      set using_gcc "yes"
 
+    if { [string match $compiler_vendor "gnu"] } {
         set gccdir [lookfor_file $tool_root_dir gcc/libgcc.a]
         if {$gccdir != ""} {
 	    set gccdir [file dirname $gccdir]
@@ -135,11 +133,6 @@ proc libffi-init { args } {
 	        }
 	    }
         }
- 
-    } else {
-
-      set using_gcc "no"
-
     }
 
     # add the library path for libffi.
@@ -278,18 +271,25 @@ proc libffi-dg-runtest { testcases default-extra-flags } {
 }
 
 proc run-many-tests { testcases extra_flags } {
-    global using_gcc
+    global compiler_vendor
-    if { [string match $using_gcc "yes"] } {
+    switch $compiler_vendor {
+      "clang" {
+	set common "-W -Wall"
+	set optimizations { "-O0" "-O1" "-O2" "-O3" "-Os" }
+      }
+      "gnu" {
         set common "-W -Wall -Wno-psabi"
         set optimizations { "-O0" "-O2" "-O3" "-Os" "-O2 -fomit-frame-pointer" }
-    } else {
+      }
+      default {
         # Assume we are using the vendor compiler.
         set common ""
         set optimizations { "" }
       }
+    }
 
     set targetabis { "" }
-    if [string match $using_gcc "yes"] {
+    if [string match $compiler_vendor "gnu"] {
         if [istarget "i?86-*-*"] {
             set targetabis {
                 ""