build: Use $(AS) for optionrom explicitly

For clang before 3.5, -fno-integrated-as does not exist,
so the workaround in 5f6f0e27fb fails to build.

Use clang's default assembler for linux-user/safe-syscall.S,
and explicitly change to use the system assembler for the
option roms.

Tested-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <rth@twiddle.net>

configure

@@ -368,6 +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}"
@@ -4490,13 +4491,6 @@ 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
 
@@ -5515,6 +5509,7 @@ 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" >> $config_host_mak
@@ -5988,6 +5983,7 @@ for rom in seabios vgabios ; do
     config_mak=roms/$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

pc-bios/optionrom/Makefile

@@ -20,6 +20,9 @@ build-all: multiboot.bin linuxboot.bin kvmvapic.bin
 # suppress auto-removal of intermediate files
 .SECONDARY:
 
+%.o: %.S
+	$(call quiet-command,$(CPP) $(QEMU_INCLUDES) $(QEMU_DGFLAGS) $(CFLAGS) -c -o - $< | $(AS) $(ASFLAGS) -o $@,"  AS    $(TARGET_DIR)$@")
+
 %.img: %.o
 	$(call quiet-command,$(LD) $(LDFLAGS_NOPIE) -Ttext 0 -e _start -s -o $@ $<,"  Building $(TARGET_DIR)$@")
 

rules.mak

@@ -69,7 +69,7 @@ LINK = $(call quiet-command, $(LINKPROG) $(QEMU_CFLAGS) $(CFLAGS) $(LDFLAGS) -o
        $(version-obj-y) $(call extract-libs,$1) $(LIBS),"  LINK  $(TARGET_DIR)$@")
 
 %.o: %.S
-	$(call quiet-command,$(CCAS) $(QEMU_INCLUDES) $(QEMU_CFLAGS) $(QEMU_DGFLAGS) $(CFLAGS) -c -o $@ $<,"  AS    $(TARGET_DIR)$@")
+	$(call quiet-command,$(CCAS) $(QEMU_INCLUDES) $(QEMU_CFLAGS) $(QEMU_DGFLAGS) $(CFLAGS) -c -o $@ $<,"  CCAS  $(TARGET_DIR)$@")
 
 %.o: %.cc
 	$(call quiet-command,$(CXX) $(QEMU_INCLUDES) $(QEMU_CXXFLAGS) $(QEMU_DGFLAGS) $(CFLAGS) $($@-cflags) -c -o $@ $<,"  CXX   $(TARGET_DIR)$@")