spirv: Generate spirv_info.c

The old table based spirv_*_to_string functions would return NULL for
any values "inside" the table that didn't have entries.  The tables also
needed to be updated by hand each time a new spirv.h was imported.
Generate the file instead.

v2: Make this script work more like src/mesa/main/format_fallback.py.
Suggested by Jason.  Remove SCons supports.  Suggested by Jason and
Emil.  Put all the build work in Makefile.nir.am in lieu of adding a new
Makefile.spirv.am.  Suggested by Emil.  Add support for Android builds
based on code provided by Emil.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Suggested-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>

src/compiler/Makefile.sources

@@ -277,12 +277,14 @@ NIR_FILES = \
 	nir/nir_worklist.c \
 	nir/nir_worklist.h
 
+SPIRV_GENERATED_FILES = \
+	spirv/spirv_info.c
+
 SPIRV_FILES = \
 	spirv/GLSL.std.450.h \
 	spirv/nir_spirv.h \
 	spirv/spirv.h \
 	spirv/spirv_info.h \
-	spirv/spirv_info.c \
 	spirv/spirv_to_nir.c \
 	spirv/vtn_alu.c \
 	spirv/vtn_cfg.c \