If PERL_NO_INLINE_FUNCTIONS is defined, don't include "inline.h"

This permits test code to include the perl headers for definitions without
creating a link dependency on the perl library (which may not exist yet).

Some of the static inline functions in inline.h reference functions in the
perl object files, and some compilers aren't smart enough to eliminate
unused static inline functions, hence including the inline.h in probe code
can cause link errors even though the probe code uses none of the functions
it declares. When probing, a failed link is taken as meaning that the
probed-for function is not present, as the assumption is that the link fails
because of it. Hence other causes of link failures cause the probing code to
generate incorrect results, and action (and bugs) at a distance.
test that perl headers don't introduce external references

This is as close as possible to the original Time::HiRes probe code,
further commits will clean that up.

[perl #116989]

[Amended from Tony's original to add -DPERL_NO_INLINE_FUNCTIONS]
remove code for non-core builds and "modernize"
support MSWin32 too
Add a "verbose" option to t/porting/extrefs.t for debugging.
Add a space after -o to keep Darwin's g++ happy, in t/porting/extrefs.t

Darwin's g++ 4.2.1 is fussy. FreeBSD's g++ 4.2.1 is not. Hateful software.
Merge in -DPERL_NO_INLINE_FUNCTIONS and t/porting/extrefs.t which tests it.