build: Use $(CCAS) for compiling .S files

We fail to pass to $(AS) all of the different flags that may be required
for a given set of CFLAGS.  Rather than figuring out the host-specific
mapping, it's better to allow the compiler driver to do that.

However, simply using $(CC) runs afoul of clang trying to build the
option roms.  C.f. 3dd46c78, wherein we changed from
using $(CC) to using $(AS) in the first place.

Work around this by passing -fno-integrated-as to clang, so that we use
the external assembler, and the clang driver still passes along all of
the options that the assembler might require.
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NRichard Henderson <rth@twiddle.net>
Message-Id: <1466703558-7723-1-git-send-email-rth@twiddle.net>

configure

@@ -368,7 +368,7 @@ else
 fi
 
 ar="${AR-${cross_prefix}ar}"
-as="${AS-${cross_prefix}as}"
+ccas="${CCAS-$cc}"
 cpp="${CPP-$cc -E}"
 objcopy="${OBJCOPY-${cross_prefix}objcopy}"
 ld="${LD-${cross_prefix}ld}"
@@ -4490,6 +4490,13 @@ if test "$fortify_source" != "no"; then
   fi
 fi
 
+#################################################
+# clang does not support the 16-bit assembly for roms
+
+if echo | $ccas -dM -E - | grep __clang__ > /dev/null 2>&1 ; then
+  ccas="$ccas -fno-integrated-as"
+fi
+
 ##########################################
 # check if struct fsxattr is available via linux/fs.h
 
@@ -5508,7 +5515,7 @@ echo "CXX=$cxx" >> $config_host_mak
 echo "OBJCC=$objcc" >> $config_host_mak
 echo "AR=$ar" >> $config_host_mak
 echo "ARFLAGS=$ARFLAGS" >> $config_host_mak
-echo "AS=$as" >> $config_host_mak
+echo "CCAS=$ccas" >> $config_host_mak
 echo "CPP=$cpp" >> $config_host_mak
 echo "OBJCOPY=$objcopy" >> $config_host_mak
 echo "LD=$ld" >> $config_host_mak
@@ -5981,7 +5988,7 @@ for rom in seabios vgabios ; do
     config_mak=roms/$rom/config.mak
     echo "# Automatically generated by configure - do not modify" > $config_mak
     echo "SRC_PATH=$source_path/roms/$rom" >> $config_mak
-    echo "AS=$as" >> $config_mak
+    echo "CCAS=$ccas" >> $config_mak
     echo "CC=$cc" >> $config_mak
     echo "BCC=bcc" >> $config_mak
     echo "CPP=$cpp" >> $config_mak

rules.mak

@@ -68,11 +68,8 @@ LINK = $(call quiet-command, $(LINKPROG) $(QEMU_CFLAGS) $(CFLAGS) $(LDFLAGS) -o
        $(call process-archive-undefs, $1) \
        $(version-obj-y) $(call extract-libs,$1) $(LIBS),"  LINK  $(TARGET_DIR)$@")
 
-%.asm: %.S
-	$(call quiet-command,$(CPP) $(QEMU_INCLUDES) $(QEMU_CFLAGS) $(QEMU_DGFLAGS) $(CFLAGS) -o $@ $<,"  CPP   $(TARGET_DIR)$@")
-
-%.o: %.asm
-	$(call quiet-command,$(AS) $(ASFLAGS) -o $@ $<,"  AS    $(TARGET_DIR)$@")
+%.o: %.S
+	$(call quiet-command,$(CCAS) $(QEMU_INCLUDES) $(QEMU_CFLAGS) $(QEMU_DGFLAGS) $(CFLAGS) -c -o $@ $<,"  AS    $(TARGET_DIR)$@")
 
 %.o: %.cc
 	$(call quiet-command,$(CXX) $(QEMU_INCLUDES) $(QEMU_CXXFLAGS) $(QEMU_DGFLAGS) $(CFLAGS) $($@-cflags) -c -o $@ $<,"  CXX   $(TARGET_DIR)$@")