c: Change T2X_* format checking macros to T23_*

Analogous to previous changes to code that matched "c2x"
(case-insensitive), also update T2X_* macros used in format checking
tables to be named T23_*.

Bootstrapped with no regressions for x86_64-pc-linux-gnu.

gcc/c-family/
	* c-format.h (T2X_UI): Rename to T23_UI.
	(T2X_UL): Rename to T23_UL.
	(T2X_ULL): Rename to T23_ULL.
	(T2X_US): Rename to T23_US.
	(T2X_UC): Rename to T23_UC.
	(T2X_ST): Rename to T23_ST.
	(T2X_UPD): Rename to T23_UPD.
	(T2X_UIM): Rename to T23_UIM.
	(T2X_D32): Rename to T23_D32.
	(T2X_D64): Rename to T23_D64.
	(T2X_D128): Rename to T23_D128.
	(T2X_I8): Rename to T23_I8.
	(T2X_I16): Rename to T23_I16.
	(T2X_I32): Rename to T23_I32.
	(T2X_I64): Rename to T23_I64.
	(T2X_U8): Rename to T23_U8.
	(T2X_U16): Rename to T23_U16.
	(T2X_U32): Rename to T23_U32.
	(T2X_U64): Rename to T23_U64.
	(T2X_IF8): Rename to T23_IF8.
	(T2X_IF16): Rename to T23_IF16.
	(T2X_IF32): Rename to T23_IF32.
	(T2X_IF64): Rename to T23_IF64.
	(T2X_UF8): Rename to T23_UF8.
	(T2X_UF16): Rename to T23_UF16.
	(T2X_UF32): Rename to T23_UF32.
	(T2X_UF64): Rename to T23_UF64.
	* c-format.cc: Update all uses of T2X_* macros to use T23_*.