FS-5819: configure fix for new clang detection

configure.in

@@ -734,16 +734,17 @@ if test x"$ac_cv_gcc_declaration_after_statement" = xyes; then
 fi
 CFLAGS="$saved_CFLAGS"
 
-# Next check added for Xcode 5 and systems with clang 5 llvm 3.3 or above, extended offset must be off
-AC_CACHE_CHECK([whether compiler supports -Wextended-offsetof], [ac_cv_clang_extended_offsetof], [
-AC_TRY_COMPILE([],[return 0;],[ac_cv_clang_extended_offsetof=yes],[ac_cv_clang_extended_offsetof=no])
-])
-AC_MSG_RESULT($ac_cv_clang_extended_offsetof)
-if test x"$ac_cv_clang_extended_offsetof" = xyes; then
-    APR_ADDTO(CFLAGS, -Wno-extended-offsetof)
+if test "x${ax_cv_c_compiler_vendor}" = "xclang" ; then
+     # Next check added for Xcode 5 and systems with clang 5 llvm 3.3 or above, extended offset must be off
+     AC_CACHE_CHECK([whether compiler supports -Wextended-offsetof], [ac_cv_clang_extended_offsetof], [
+       AC_TRY_COMPILE([],[return 0;],[ac_cv_clang_extended_offsetof=yes],[ac_cv_clang_extended_offsetof=no])
+     ])
+     AC_MSG_RESULT($ac_cv_clang_extended_offsetof)
+     if test x"$ac_cv_clang_extended_offsetof" = xyes; then
+         APR_ADDTO(CFLAGS, -Wno-extended-offsetof)
+     fi
 fi
 
-
 # Tested and fixed lot of modules, but some are untested.  Will be added back when the core team decide it ready
 # Untested modules : mod_osp mod_soundtouch mod_sangoma_codec mod_dingaling mod_opal mod_skypopen mod_h323 mod_khomp 
 #                    mod_unimrcp mod_cepstral mod_erlang_event mod_snmp mod_perl mod_java mod_managed