This is a bit more consistent with the naming of the other header files
(openlibm_complex.h and openlibm_fenv.h). Re-add an openlibm.h header
that includes all of the public headers as a shorthand.
Fix up all of the source files to include <openlibm_math.h> instead of
<openlibm.h>. While there, fix ordering of the includes.
Unlike the __weak_reference() macro, __strong_reference() does type
checking. It can only create the reference if the type of the source and
the destination function match exactly.
Even if double == long double in practice, they remain unequal at the
language level.
OpenLibm uses the __weak_reference() macro for platforms where double
and long double use the same layout. That way functions only need to be
provided by the library once. The point is, in this specific case we
want to use strong references; not weak references.
Strong references can be used to give a symbol a second name. If you
look at the resulting object file, you will have two symbols with the
same offset and size. Weak references are different, in the sense that
they are marked in such a way that they act as fallbacks. They are only
used if an explicitly matching symbol is missing.
Put external headers before internal ones. While there, replace a lot of
occurences of "openlibm.h" with <openlibm.h>. It should be thought of as
an external header, as it is installed along with the library.
