Fixes #8783.

In order to avoid querying the nm version that does not work on Mac OS X
we use the "nm -P" output that is supposed to produce (more portable)
POSIX output and works on all tested OSes (MinGW, Mac OS X, Solaris and
Linux using GNU nm) although slightly different (as documented). The "nm
-P" output is actually only needed to recognize the output of a non-GNU
Solaris nm (all other OSes produce sane outut using "nm" only).

Signed-off-by: Austin Seipp <austin@well-typed.com>