msvcrt: Don't depend on the system's implementation of acos () & asin().

[Dan Kegel]

Henri wrote:
> glibc implements acos() as the FPU equivalent of atan2(sqrt(1 - x ^ 2), x).

I just looked, and there are several implementations of acos
in glibc, and they all seem to very carefully choose
how to do it based on how close x is to 1.

> This should be fixed on the glibc side as well

Indeed.  Have you filed a bug report against glibc yet?
I didn't see one at http://sourceware.org/bugzilla/
Please be sure to attach a simple C program that
reproduces the problem, or better yet, a patch
to add a test case to their test suite.