Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC r230391, r230400, 231019:

This commit adds profiling support for powerpc64. Now we can do application
profiling and kernel profiling. To enable kernel profiling one has to build
kgmon(8). I will enable the build once I managed to build and test powerpc
(32-bit) kernels with profiling support.

- add a powerpc64 PROF_PROLOGUE for _mcount.
- add macros to avoid adding the PROF_PROLOGUE in certain assembly entries.
- apply these macros where needed.
- add size information to the MCOUNT function.

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Turn off default generation of userland dot symbols on powerpc64 now that
we have a binutils that supports it. Kernel dot symbols remain on to assist
DDB.

Mark assembler sources from libc as working with non-executable stack.

Reviewed and tested by: nwhitehorn

Fix stack alignment (required to be to 16 bytes) instead of ptrace and
cerror on powerpc64.

Provide 64-bit PowerPC support in libc.

Obtained from: projects/ppc64