ldbl-128ibm-compat: Create libm-alias-float128.h

Add a new libm-alias-float128.h in order to provide the __*ieee128
aliases for the existing *f128 that do not have a globally exported
symbol.

	* sysdeps/ieee754/ldbl-128ibm-compat/Versions: New file.
	* sysdeps/ieee754/ldbl-128ibm-compat/libm-alias-float128.h: New file.