Avoid compilation errors with MSVC option -fp:strict.

Avoid compilation errors with MSVC option -fp:strict.

* lib/floor.c: Use MSVC specific pragma fenv_access.
* lib/ceil.c: Likewise.
* lib/trunc.c: Likewise.
* lib/round.c: Likewise.
* lib/rint.c: Likewise.
* lib/fma.c: Likewise.
* lib/integer_length.c: Likewise.
* m4/round.m4 (gl_FUNC_ROUND): Likewise.
* m4/roundf.m4 (gl_FUNC_ROUNDF): Likewise.
* tests/test-floor2.c: Likewise.
* tests/test-floorf2.c: Likewise.
* tests/test-ceil2.c: Likewise.
* tests/test-ceilf2.c: Likewise.
* tests/test-trunc2.c: Likewise.
* tests/test-truncf2.c: Likewise.
Reported by Michael Goffioul <michael.goffioul@gmail.com>.