Hexagon (target/hexagon) generator phase 3 - C preprocessor for decode tree

Hexagon (target/hexagon) generator phase 3 - C preprocessor for decode tree

Run the C preprocessor across the instruction definition and encoding
files to expand macros and prepare the iset.py file.  The resulting
fill contains python data structures used to build the decode tree.

Signed-off-by: Taylor Simpson <tsimpson@quicinc.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <1612763186-18161-22-git-send-email-tsimpson@quicinc.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>