Largely based on MySQL commit
https://github.com/mysql/mysql-server/commit/75271e51d60bce8683423b208cbb43b11ca6060e

MySQL Ref:
    BUG#24566529: BACKPORT BUG#23575445 TO 5.6

    (cut)
    Also, the PTR_SANE macro which tries to check if a pointer
    is invalid (used when printing pointer values in stack traces)
    gave false negatives on OSX/FreeBSD. On these platforms we
    now simply check if the pointer is non-null. This also removes
    a sbrk() deprecation warning when building on OS X. (It was
    before only disabled with building using XCode).

Removed execinfo path of MySQL patch that was already included.

sbrk doesn't exist on FreeBSD aarch64.

Removed HAVE_BSS_START based detection and replaced with __linux__
as it doesn't exist on OSX, Solaris or Windows.  __bss_start
exists on mutiple Linux architectures.

Tested on FreeBSD and Linux x86_64. Being in FreeBSD ports for 2
years implies a good testing there on all FreeBSD architectures there
too. MySQL-8.0.21 code is functionally identical to original commit.