libgcrypt fails to build with clang

[tstellar]

random/jitterentropy-base.c relies on the gcc behavior that the OPTIMIZE macro is undefined when using #pragma GCC optimize ("O0"). The clang equivalent to this: #pragma clang optimize off, does not undefine the OPTIMIZE macro.

Upstream Patch/Discussion: http://gnupg.10057.n7.nabble.com/PATCH-Fix-build-of-jitterentropy-base-c-with-clang-td70843.html

[tpgxyz]

In OpenMandriva we fixed it same way long time ago:
https://github.com/OpenMandrivaAssociation/libgcrypt/blob/master/libgcrypt-1.8.3-fix-clang-optimization.patch