c: Handle C23 floating constant {d,D}{32,64,128} suffixes like {df,dd,dl}

c: Handle C23 floating constant {d,D}{32,64,128} suffixes like {df,dd,dl}

C23 roughly says that {d,D}{32,64,128} floating point constant suffixes
are alternate spellings of {df,dd,dl} suffixes in annex H.

So, the following patch allows that alternate spelling.
Or is it intentional it isn't enabled and we need to do everything in
there first before trying to define __STDC_IEC_60559_DFP__?
Like add support for _Decimal32x and _Decimal64x types (including
the d32x and d64x suffixes) etc.

2024-11-13  Jakub Jelinek  <jakub@redhat.com>

libcpp/
	* expr.cc (interpret_float_suffix): Handle d32 and D32 suffixes
	for C like df, d64 and D64 like dd and d128 and D128 like
	dl.
gcc/c-family/
	* c-lex.cc (interpret_float): Subtract 3 or 4 from copylen
	rather than 2 if last character of CPP_N_DFLOAT is a digit.
gcc/testsuite/
	* gcc.dg/dfp/c11-constants-3.c: New test.
	* gcc.dg/dfp/c11-constants-4.c: New test.
	* gcc.dg/dfp/c23-constants-3.c: New test.
	* gcc.dg/dfp/c23-constants-4.c: New test.