Reviewed-by: shenwei

presumably internal code (ungetwc and fputwc) was written assuming a
macro implementation existed; otherwise use of isascii is just a
pessimization.

the casts of the argument to unsigned int suppressed diagnosis of
errors like passing a pointer instead of a character. putting the
actual function call in an unreachable branch restores any diagnostics
that would be present if the macros didn't exist and functions were
used.

based on patch by Sergey Dmitrouk.

isspace can be a bottleneck in a simple parser, inlining it
gives slightly smaller and faster code

src/locale/pleval.o already had this optimization, the size
change for other libc functions for i386 is

src/internal/intscan.o     2134    2118   -16
src/locale/dcngettext.o    1562    1552   -10
src/network/res_msend.o    1961    1940   -21
src/network/lookup_name.o  2627    2608   -19
src/network/getnameinfo.o  1814    1811    -3
src/network/lookup_serv.o   643     624   -19
src/stdio/vfscanf.o        2675    2663   -12
src/stdlib/atoll.o          117     107   -10
src/stdlib/atoi.o            95      91    -4
src/stdlib/atol.o            95      91    -4
src/time/strptime.o        1515    1503   -12
(TOTALS)                 432451  432321  -130

the old behavior of exposing nothing except plain ISO C can be
obtained by defining __STRICT_ANSI__ or using a compiler option (such
as -std=c99) that predefines it. the new default featureset is POSIX
with XSI plus _BSD_SOURCE. any explicit feature test macros will
inhibit the default.

installation docs have also been updated to reflect this change.

patch by Isaac Dunham. matched closely (maybe not exact) to glibc's
idea of what _BSD_SOURCE should make visible.

patch by Arvid Picciani (aep)

issue reported by nsz, but it's actually not just pedantic. the
functions can take input of any arithmetic type, including floating
point, and the behavior needs to be as if the conversion implicit in
the function call took place.

thanks to Peter Mazinger (psm) for pointing many of these issues out
and submitting a patch on which this commit is loosely based