This local copy of a SHA1 implementation based on the sources below.

Why:
 - Some libraries suffer from race condition and other issues. For example see
commit ade3108bb5b0 ("util: Fix race condition on libgcrypt initialization").

 - Fold the handling and detection of _eight_ implementations at configure
stage and _seven_ different codepaths.

 - Have a single, uniform, code used by developers, testers and users.

 - Avoid conflicts when using software which ships with it's own SHA1 library.
The latter of which conflicting with the one mesa is build against.



Source:
The SHA1 implementation is copied verbatim from the following links.
At the time of checkout HEAD is 1.25 and 1.24 respectively.

http://cvsweb.openbsd.org/cgi-bin/cvsweb/~checkout~/src/lib/libc/hash/sha1.c?rev=HEAD
http://cvsweb.openbsd.org/cgi-bin/cvsweb/~checkout~/src/include/sha1.h?rev=HEAD


Notes:
 - The files should not have any local changes. If there are any they should be
clearly documented below and one should aim to upstream them where possible.

 - Files will be periodically syncronised with the respective upstream sources.
Updates will be made regularly, but since the code is _not_ aimed as a
cryptography solution any issues found should not be considered security ones.


Local changes:
 - Removed __bounded__ attribute qualifiers. Unavailable on platforms targeted
by Mesa. Upstream status: TBD (N/A ?)

 - Pick the sha1.h header from the current folder, by using "" over <> in the
include directive. Upstream status: TBD

 - Remove unused function prototypes - SHA1End, SHA1File, SHA1FileChunk and
SHA1Data. Upstream status: TBD

 - Use stdint.h integer types - u_int{8,16,32}_t -> uint{8,16,32}_t and
u_int -> uint32_t, change header include. Upstream status: TBD

 - Revert sha1.c rev 1.26 change (introduce DEF_WEAK).
Upstream status: TBD (N/A ?)

 - Add stdint.h include in sha1.h for uint*_t types. Upstream status: TBD

 - Add stddef.h include in sha1.h for size_t type. Upstream status: TBD

 - Use memset over explicit_bzero, since memset_s once isn't widely available.
Upstream status: TBD (N/A ?)

 - Manually expand __BEGIN_DECLS/__END_DECLS and make sure that they include
the struct declaration.
Upstream status: TBD

 - Add non-typedef struct name.
Upstream status: TBD
