Modify build_tools/build_detect_platform to detect and set -march=z10 on Linux s390x.

build_tools/build_detect_platform

@@ -360,13 +360,13 @@ fi
 if test "$USE_SSE"; then
   # if Intel SSE instruction set is supported, set USE_SSE=1
   COMMON_FLAGS="$COMMON_FLAGS -msse -msse4.2 "
-elif [ "$TARGET_ARCHITECTURE" = s390x ]; then
-  COMMON_FLAGS="$COMMON_FLAGS -march=z10 "
 elif test -z "$PORTABLE"; then
   if test -n "`echo $TARGET_ARCHITECTURE | grep ^ppc64`"; then
     # Tune for this POWER processor, treating '+' models as base models
     POWER=`LD_SHOW_AUXV=1 /bin/true | grep AT_PLATFORM | grep -E -o power[0-9]+`
     COMMON_FLAGS="$COMMON_FLAGS -mcpu=$POWER -mtune=$POWER "
+  elif test -n "`echo $TARGET_ARCHITECTURE | grep ^s390x`"; then
+    COMMON_FLAGS="$COMMON_FLAGS -march=z10 "
   else
     COMMON_FLAGS="$COMMON_FLAGS -march=native "
   fi