[Darwin, PPC] Check for out of range asm values.

[Darwin, PPC] Check for out of range asm values.

There are some cases in which the value for the max skip to a p2align
directive can be negative.  The older assembler just ignores these cases
where newer tools produce an error.  To preserve behaviour, we avoid
emitting out of range values.

gcc/ChangeLog:

2019-10-23  Iain Sandoe  <iain@sandoe.co.uk>

	* config/rs6000/darwin.h (ASM_OUTPUT_MAX_SKIP_ALIGN): Guard
	against out of range max skip or log values.

From-SVN: r277307