gallivm: print declarations of intrinsics with GALLIVM_DEBUG=ir
gallivm: print declarations of intrinsics with GALLIVM_DEBUG=ir

Those aren't really interesting, however outputting them is helpful when
trying to feed the IR to llvm llc (or opt) for debugging.

Reviewed-by: Jose Fonseca <61b5a29db2c0650f7c8510f93eece059c1b09320@vmware.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler