Fix include guards in regex and utime

See merge request redox-os/relibc!176

The include_guard in both regex and utime was "_TEMPLATE_H", this meant that including both wasn't possible.
Their header guards should be consistent with the header files as well.
Changed _TEMPLATE_H to _REGEX_H and _UTIME_H in /regex/cbindgen.toml and /utime/cbindgen.toml respectively.

Implement libgen.h

See merge request redox-os/relibc!175

Implemented the following calls according to http://pubs.opengroup.org/onlinepubs/7908799/xsh/libgen.h.html
- char* basename(char*)
- char* dirname(char*)

Added test suit for the implemented calls.

Issue: redox-os/relibc#134

Handle getopt reinitialization

See merge request redox-os/relibc!174

Disable symbol mangling for C++

See merge request redox-os/relibc!173

Fix assert when used as an expression

See merge request redox-os/relibc!172

Based on what musl does.

Don't drop the host aliases pointer vector in `gethostent`

Closes #130

See merge request redox-os/relibc!170

Implement almost all of printf

See merge request redox-os/relibc!171

There are pointers to this vector in `HOST_ENTRY` so we must keep it around for
as long as `HOST_ENTRY` exists.