Don't build 32-bit libatomic with -march=i486 on x86-64

Gcc uses the same -march= for both -m32 and -m64 on x86-64 unless
--with-arch-32= is used.  There is no need for -march=i486 to compile
32-bit libatomic on x86-64.

	PR target/70454
	* configure.tgt (XCFLAGS): Don't add -march=i486 to compile
	32-bit x86 target library on x86-64.

From-SVN: r235287

libatomic/ChangeLog

+2016-04-20  H.J. Lu  <hongjiu.lu@intel.com>
+
+	PR target/70454
+	* configure.tgt (XCFLAGS): Don't add -march=i486 to compile
+	32-bit x86 target library on x86-64.
+
 2016-01-06  Szabolcs Nagy  <szabolcs.nagy@arm.com>
 
 	PR other/67627

libatomic/configure.tgt

@@ -81,14 +81,8 @@ case "${target_cpu}" in
 	try_ifunc=yes
 	;;
   x86_64)
-	case " ${CC} ${CFLAGS} " in
-	  *" -m32 "*)
-	    XCFLAGS="${XCFLAGS} -march=i486 -mtune=generic"
-	    XCFLAGS="${XCFLAGS} -fomit-frame-pointer"
-	    ;;
-	  *)
-	    ;;
-	esac
+	# x86_64 compiler passes -march=x86_64 by default when building
+	# 32bit target libraries.
 	ARCH=x86
 	# ??? Detect when -mcx16 is already enabled.
 	try_ifunc=yes