Revert "build/libgnuregex: Remove."

This reverts commit ca087b05323d3c05f7fe807df017ce4133604b67.

Mac OS X requires libgnuregex for Keymap

libgnuregex: fix debug build.

Add missing "printchar.c", which is only used in DEBUG mode. The
function was recovered from original regex sources.

Note that the gnu regexp library is deprecated, and so is its
replacement, gnu rx. GNU suggests using the regex implementation from
the glibc, but that one isn't as portable.

Thanks to Andrew Lindesay for the investigations and initial patch!

Fixes #12952.

BPackageInfo::Parser: Validate URL strings.

Fixes #12710.

Signed-off-by: Augustin Cavalier <waddlesplash@gmail.com>
I fixed the modifications to the Jamfiles in src/bin, they were all wrong
in the patch.

Import gnuregex 0.12 and remove hardcoded paths

This is required on OS X and other systems which do not have the glibc
extensions for regular expressions (FreeBSD is not one of them as it
already includes gnuregex in /usr). With this there are no hardcoded
non-standard paths for OS X anymore.

regex.c and regex.h are from the official gnuregex 0.12 distribution,
the only modification is that I added __BEGIN_DECLS and __END_DECLS to
regex.h.

Import gnuregex 0.12 and remove hardcoded paths

This is required on OS X and other systems which do not have the glibc
extensions for regular expressions (FreeBSD is not one of them as it
already includes gnuregex in /usr). With this there are no hardcoded
non-standard paths for OS X anymore.

regex.c and regex.h are from the official gnuregex 0.12 distribution,
the only modification is that I added __BEGIN_DECLS and __END_DECLS to
regex.h.