asinf: Avoid redefinition error on MSVC. * m4/math_h.m4 (gl_MATH_H_DEFAULTS): Define REPLACE_ASINF. * m4/asinf.m4 (gl_FUNC_ASINF): Set REPLACE_ASINF to 1 if the function may be defined as an inline function. * modules/math (Makefile.am): Substitute REPLACE_ASINF. * lib/math.in.h (asinf): Override if REPLACE_ASINF is 1.