. Add s_erfl.c to building libm.
. Add MLINKS for erfl.3 and erfcl.3.
* Symbol.map:
. Move erfl and erfcl to their proper location.
* ld128/s_erfl.c:
. Implementations of erfl and erfcl in the IEEE 754 128-bit format.
* ld80/s_erfl.c:
. Implementations of erfl and erfcl in the Intel 80-bit format.
* man/erf.3:
. Document the new functions.
. While here, remove an incomplete sentence.
* src/imprecise.c:
. Remove the stupidity of mapping erfl and erfcl to erf and erfc.
* src/math.h:
. Move the declarations of erfl and erfcl to their proper place.
* src/s_erf.c:
. For architectures where double and long double are the same
floating point format, use weak references to map erfl to
erf and ercl to erfc.
Reviewed by: bde (many earlier versions)
