Allow --with-cpu/--with-tune for !arm.

The configure error mentioned in the commits that disable
--with-arch/--with-tune when --with-cpu is specified is specific to ARM
builds. For other architectures, it makes sense (hey, it even makes
sense for ARM - read 'info gcc'! - it is just a shortcoming of ARM
build, apparently).

Thus, add an arch setting ARCH_EXCLUSIVE_WITH_CPU (currently, set only
for ARM) that will trigger current behavior. Permit combinations of
--with-arch/cpu/tune for other arches.

Signed-off-by: Alexey Neyman <stilor@att.net>

config/arch/arm.in

@@ -9,6 +9,7 @@
 ## select ARCH_DEFAULT_LE
 ## select ARCH_SUPPORTS_WITH_ARCH
 ## select ARCH_SUPPORTS_WITH_CPU
+## select ARCH_EXCLUSIVE_WITH_CPU
 ## select ARCH_SUPPORTS_WITH_TUNE
 ## select ARCH_SUPPORTS_WITH_FLOAT if ARCH_32
 ## select ARCH_SUPPORTS_WITH_FPU if ARCH_32

config/target.in

@@ -210,11 +210,14 @@ config ARCH_SUPPORTS_WITH_FPU
 config ARCH_SUPPORTS_SOFTFP
     bool
 
+config ARCH_EXCLUSIVE_WITH_CPU
+    bool
+
 config ARCH_ARCH
     string
     prompt "Architecture level"
     depends on ARCH_SUPPORTS_WITH_ARCH
-    depends on ARCH_CPU = ""
+    depends on !ARCH_EXCLUSIVE_WITH_CPU || ARCH_CPU = ""
     default ""
     help
       GCC uses this name to determine what kind of instructions it can emit
@@ -271,7 +274,7 @@ config ARCH_TUNE
     string
     prompt "Tune for CPU"
     depends on ARCH_SUPPORTS_WITH_TUNE
-    depends on ARCH_CPU = ""
+    depends on !ARCH_EXCLUSIVE_WITH_CPU || ARCH_CPU = ""
     default ""
     help
       This option is very similar to the ARCH_CPU option (above), except