s390: only build for new CPUs with clang

llvm does does not understand -march=z9-109 and older target
specifiers, so disable the respective Kconfig settings and
the logic to make the boot code work on old systems when
building with clang.

Part of the early boot code is normally compiled with -march=z900
for maximum compatibility. This also has to get changed with
clang to the oldest supported ISA, which is -march=z10 here.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/Kconfig

@@ -241,6 +241,7 @@ choice
 
 config MARCH_Z900
 	bool "IBM zSeries model z800 and z900"
+	depends on !CC_IS_CLANG
 	select HAVE_MARCH_Z900_FEATURES
 	help
 	  Select this to enable optimizations for model z800/z900 (2064 and
@@ -249,6 +250,7 @@ config MARCH_Z900
 
 config MARCH_Z990
 	bool "IBM zSeries model z890 and z990"
+	depends on !CC_IS_CLANG
 	select HAVE_MARCH_Z990_FEATURES
 	help
 	  Select this to enable optimizations for model z890/z990 (2084 and
@@ -257,6 +259,7 @@ config MARCH_Z990
 
 config MARCH_Z9_109
 	bool "IBM System z9"
+	depends on !CC_IS_CLANG
 	select HAVE_MARCH_Z9_109_FEATURES
 	help
 	  Select this to enable optimizations for IBM System z9 (2094 and
@@ -348,12 +351,15 @@ config TUNE_DEFAULT
 
 config TUNE_Z900
 	bool "IBM zSeries model z800 and z900"
+	depends on !CC_IS_CLANG
 
 config TUNE_Z990
 	bool "IBM zSeries model z890 and z990"
+	depends on !CC_IS_CLANG
 
 config TUNE_Z9_109
 	bool "IBM System z9"
+	depends on !CC_IS_CLANG
 
 config TUNE_Z10
 	bool "IBM System z10"

arch/s390/boot/Makefile

@@ -12,18 +12,24 @@ KBUILD_AFLAGS := $(KBUILD_AFLAGS_DECOMPRESSOR)
 KBUILD_CFLAGS := $(KBUILD_CFLAGS_DECOMPRESSOR)
 
 #
-# Use -march=z900 for als.c to be able to print an error
+# Use minimum architecture for als.c to be able to print an error
 # message if the kernel is started on a machine which is too old
 #
-ifneq ($(CC_FLAGS_MARCH),-march=z900)
+ifndef CONFIG_CC_IS_CLANG
+CC_FLAGS_MARCH_MINIMUM := -march=z900
+else
+CC_FLAGS_MARCH_MINIMUM := -march=z10
+endif
+
+ifneq ($(CC_FLAGS_MARCH),$(CC_FLAGS_MARCH_MINIMUM))
 AFLAGS_REMOVE_head.o		+= $(CC_FLAGS_MARCH)
-AFLAGS_head.o			+= -march=z900
+AFLAGS_head.o			+= $(CC_FLAGS_MARCH_MINIMUM)
 AFLAGS_REMOVE_mem.o		+= $(CC_FLAGS_MARCH)
-AFLAGS_mem.o			+= -march=z900
+AFLAGS_mem.o			+= $(CC_FLAGS_MARCH_MINIMUM)
 CFLAGS_REMOVE_als.o		+= $(CC_FLAGS_MARCH)
-CFLAGS_als.o			+= -march=z900
+CFLAGS_als.o			+= $(CC_FLAGS_MARCH_MINIMUM)
 CFLAGS_REMOVE_sclp_early_core.o	+= $(CC_FLAGS_MARCH)
-CFLAGS_sclp_early_core.o	+= -march=z900
+CFLAGS_sclp_early_core.o	+= $(CC_FLAGS_MARCH_MINIMUM)
 endif
 
 CFLAGS_sclp_early_core.o += -I$(srctree)/drivers/s390/char