Make macro checks ARMv8-M baseline proof

libgloss:

        * arm/Makefile.in: Add newlib/libc/machine/arm to the include path if
        newlib is present.
        * arm/arm.h: Include acle-compat.h.
        (THUMB_V7_V6M): Rename to ...
        (PREFER_THUMB): This.  Use ACLE macros __ARM_ARCH_ISA_ARM instead of
        __ARM_ARCH_6M__ to decide whether to define it.
        (THUMB1_ONLY): Define for Thumb-1 only targets.
        (THUMB_V7M_V6M): Rename to ...
        (THUMB_VXM): This.  Defined based on __ARM_ARCH_ISA_ARM, excluding
        ARMv7.
        * arm/crt0.S: Use THUMB1_ONLY rather than __ARM_ARCH_6M__,
        !__ARM_ARCH_ISA_ARM rather than THUMB_V7M_V6M for fp enabling, and
        PREFER_THUMB rather than THUMB_V7_V6M.  Rename other occurences of
        THUMB_V7M_V6M to THUMB_VXM.
        * arm/linux-crt0.c: Likewise.
        * arm/redboot-crt0.S: Likewise.
        * arm/swi.h: Likewise.
        * arm/trap.S: Likewise.

newlib:

        * libc/machine/arm/memcpy-stub.c: Use ACLE macros __ARM_ARCH_ISA_THUMB
        and __ARM_ARCH_ISA_ARM to check for Thumb-2 only targets rather than
        __ARM_ARCH and __ARM_ARCH_PROFILE.
        * libc/machine/arm/memcpy.S: Likewise.
        * libc/machine/arm/setjmp.S: Likewise for Thumb-1 only target and
        include acle-compat.h.
        * libc/machine/arm/strcmp.S: Likewise for Thumb-1 and Thumb-2 only
        target and include acle-compat.h.
        * libc/sys/arm/arm.h: Include acle-compat.h.
        (THUMB_V7_V6M): Rename to ...
        (PREFER_THUMB): This.  Use ACLE macro __ARM_ARCH_ISA_ARM instead of
        __ARM_ARCH_6M__ to decide whether to define it.
        (THUMB1_ONLY): Define for Thumb-1 only targets.
        (THUMB_V7M_V6M): Rename to ...
        (THUMB_VXM): This.  Defined based on __ARM_ARCH_ISA_ARM, excluding
        ARMv7.
        * libc/sys/arm/crt0.S: Use PREFER_THUMB rather than THUMB_V7_V6M and
        rename THUMB_V7M_V6M into THUMB_VXM.
        * libc/sys/arm/swi.h: Likewise.

libgloss/arm/linux-crt0.c

@@ -12,7 +12,7 @@
 
 static int _main(int argc, char *argv[]) __attribute__((noreturn));
 
-#if defined(__thumb__) && !defined(THUMB_V7_V6M)
+#if __thumb__ && !defined(PREFER_THUMB)
 asm("\n"
 	".code 32\n"
 	".global _start\n"