PR target/107299: Update IEEE 128-bit types for PowerPC libgcc

PR target/107299: Update IEEE 128-bit types for PowerPC libgcc

This patch updates the IEEE 128-bit types in libgcc.

At the moment, we cannot build GCC when the target uses IEEE 128-bit long
doubles, such as building the compiler for a native Fedora 36 system.  The
build dies when it is trying to build the _mulkc3.c and _divkc3 modules.

This patch changes the IEEE 128-bit type (TFtype) in the IEEE 128-bit support
to use either _Float128 or long double.  Previously we would use the __float128
type.  In addition, the TCtype will use the same type along with _Complex.

I changed the libgcc build so that the IEEE 128-bit support is now compiled
with -mabi=ieeelongdouble.  For the _mulkc3 and _divkc3, I explicitly use long
double and long double _Complex to avoid type mismatch errors.

While it is desirable to ultimately have __float128 and _Float128 use the same
internal type and mode within GCC, at present if you use the option
-mabi=ieeelongdouble, the __float128 type will use the long double type.  We
get an internal compiler error if we combine the signbitf128 built-in with a
long double type.

I've gone through several iterations of trying to fix this within GCC, and
there are various problems that have come up.  I developed this alternative
patch that changes libgcc so that it does not tickle the issue.  I hope we can
fix the compiler at some point, but right now, this is preventing people on
Fedora 36 systems from building compilers where the default long double is IEEE
128-bit.

2023-01-12   Michael Meissner  <meissner@linux.ibm.com>

	PR target/107299
	* config/rs6000/_divkc3.c (toplevel): Add assertion for building with
	-mabi=ieeelongdouble.  Remove code supporting -mabi=ibmlongdouble.
	(COPYSIGN): Use the long double built-in.
	(INFINITY): Likewise.
	(FABS): Likewise.
	(_divkc3): Use long double and _Complex long double types.
	* config/rs6000/_mulkc3.c (toplevel): Add assertion for building with
	-mabi=ieeelongdouble.
	(COPYSIGN): Use the long double built-in.
	(INFINITY): Likewise.
	(_mulkc3): Use long double and _Complex long double types.
	* config/rs6000/quad-float128.h (TF): Delete definition.
	(TFtype): Define to be _Float128 or long double.
	(TCtype): Define to be _Complex _Float128 or _Complex long double.
	(__mulkc3_sw): Only declare function if -mabi=ieeelongdouble.
	(__divkc3_sw): Likewise.
	(__mulkc3_hw): Likewise.
	(__divkc3_hw): Likewise.
	(__mulkc3): Likewise.
	(__divkc3): Likewise.
	* config/rs6000/t-float128 (FP128_CFLAGS_SW): Use -mabi=ieeelongdouble.
	* config/rs6000/t-float128-hw (FP128_CFLAGS_HW): Likewise.
	* libgcc2.h (TFtype): Allow MD code to override definition.
	(TCtype): Likewise.
	* soft-fp/quad.h (TFtype): Likewise.