Commit 69f4c4029183fb26d2fcae00790881620c1978a3 improved most
macro checks to be ARMv8-M baseline proof, but missed a few
occurrences which otherwise fail to build when using a CPU setting
such as cortex-m0 or cortex-m23. This patch brings the same
changes as the ones that were committed to libgloss at that time.
newlib:
* libc/sys/arm/crt0.S: Use THUMB1_ONLY rather than
__ARM_ARCH_6M__.