libquadmath: Fix up libquadmath/math/sqrtq.c compilation in some powerpc* configurations [PR116007]

My PR114623 change started using soft-fp.h and quad.h for the sqrtq implementation.
Unfortunately, that seems to fail building in some powerpc* configurations, where
TFmode isn't available.
quad.h has:
 #ifndef TFtype
 typedef float TFtype __attribute__ ((mode (TF)));
 #endif
and uses TFtype.  quad.h has:
 /* Define the complex type corresponding to __float128
    ("_Complex __float128" is not allowed) */
 #if (!defined(_ARCH_PPC)) || defined(__LONG_DOUBLE_IEEE128__)
 typedef _Complex float __attribute__((mode(TC))) __complex128;
 #else
 typedef _Complex float __attribute__((mode(KC))) __complex128;
 #endif
with the conditional and KCmode use added during porting of libquadmath
to powerpc*, so I've just defined TFtype for powerpc when __LONG_DOUBLE_IEEE128__
isn't defined; I could define it to float __attribute__ ((mode (KF))) but it
seemed easier to just define it to __float128 which should do the same thing.

2024-08-03  Jakub Jelinek  <jakub@redhat.com>

	PR target/116007
	* math/sqrtq.c (TFtype): For PowerPC without __LONG_DOUBLE_IEEE128__
	define to __float128 before including soft-fp.h and quad.h.