add inline isspace in ctype.h as an optimization

add inline isspace in ctype.h as an optimization

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