* libc/ctype/ctype_cp.h: Mark non-cased letters in tables for codepages
720, 862, 874, 1255, and 1256 to _U|_L. Fix a couple of incorrect
class mappings.
* libc/ctype/ctype_iso.h: Mark non-cased letters in ISO-8859 tables
6, 8, and 11 to _U|_L. Fix a couple of incorrect class mappings.
* libc/ctype/isblank.c (isblank): Special case TAB.
* libc/ctype/islower.c (islower): Check explicitely for _L flag only
in (_U|_L).
* libc/ctype/isupper.c (isupper): Ditto, but check for _U flag.
* libc/include/ctype.h (islower): Same in macro.
(isupper): Ditto.
(isblank): Special case TAB. Redefine macro for GCC only.
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