regcomp, regexec, fnmatch: avoid array bounds read error

regcomp, regexec, fnmatch: avoid array bounds read error

* lib/regcomp.c (build_equiv_class): From glibc:
Use only the low 24 bits of a findidx return value as an index
into the weights array.  Patch by Ulrich Drepper:
http://sourceware.org/git/gitweb.cgi?p=glibc.git;a=commit;h=b7d1c5fa30
* lib/regexec.c (check_node_accept_bytes): Likewise.
* lib/fnmatch_loop.c (FCT): Likewise.