Revert "sv_grow: performance improvement for short strings"

This reverts commit 880c169bb2bd5e6e9ae996842d6860bf88d28585.
fix fp_classify in perl.h for VMS.

We have to include <fp.h> as well for the macros we're testing
for to be defined.
Some missing c99_xxx functions for POSIX.xs on VMS.
Do not use HUGE_VAL/VALL for NV_INF.

Because some platforms (like HP-UX 10.*) have HUGE_VAL as DBL_MAX,
which, while large, is not quite the infinity.  So have infinity
own our very own.

Similarly for NV_NAN.
Perl_isinf and Perl_isfinite fallbacks.

(We have so many fallbacks that some of them probably never deploy.)
Use Perl_isfinite() to guard the frexpl.

Also, print out the deadly nv.
HP-UX: 10.20 math functions don't generate infinities.

So skip the tests that attempt creating such.
HP-UX: 10.X doesn't really have isfinite().
HP-UX: missing C99 math.
POSIX math: M_LN10 was missing.
POSIX math: Initialize RETVAL to NV_NAN/-1.
POSIX math: define the fpclassify returns always if needed.

(Even without HAS_FPCLASSIFY.)
POSIX math: Perl_ldexp, not Perl_ldexpl.
POSIX math: First cut at C99 math docs.

Undoubtedly stuff missing and incorrect.  And typod.
lib/utf8_heavy.pl: Don't return empty under miniperl

When run under miniperl before mktables has generated its tables , this
program would return empty for Unicode properties instead of an error
condition.  The problem was that when it detected this, it just
continued on to the rest of the code which assumed it had found an empty
table, instead of no table at all.  The solution is to return an e error
when one is detected.
Update ExtUtils::CBuilder to version 0.280219. Correct one test.

Switch to using VERSION_FROM in Makefile.PL.

For: RT #122675

Add update to ExtUtils::CBuilder to perldelta.
Static initialization using 1/0 or 0/0 not C89.
HP-UX: more robust (10.X) and verbose test skippage.
Ignore warning about unused result since it is desperation time.
POSIX math: problems found in Win32.