Add list of potential target datatype comments to SYSTEM.def

Add list of potential target datatype comments to SYSTEM.def

Add list of potential target datatype comments to all SYSTEM.def
files to improve usefulness of target independent documentation.

gcc/m2/ChangeLog:

	* gm2-libs-coroutines/SYSTEM.def: Added list of data types.
	* gm2-libs-iso/SYSTEM.def: Added list of data types.
	* gm2-libs/SYSTEM.def: Added list of data types.
	* target-independent/SYSTEM-iso.texi: Rebuilt.
	* target-independent/SYSTEM-pim.texi: Rebuilt.
	* target-independent/gm2-libs.texi: Rebuilt.

Signed-off-by: Gaius Mulley <gaiusmod2@gmail.com>