math: remove STRICT_ASSIGN macro

gcc did not always drop excess precision according to c99 at assignments
before version 4.5 even if -std=c99 was requested which caused badly
broken mathematical functions on i386 when FLT_EVAL_METHOD!=0

but STRICT_ASSIGN was not used consistently and it is worked around for
old compilers with -ffloat-store so it is no longer needed

the new convention is to get the compiler respect c99 semantics and when
excess precision is not harmful use float_t or double_t or to specialize
code using FLT_EVAL_METHOD

src/internal/libm.h

@@ -155,15 +155,4 @@ long double __tanl(long double, long double, int);
 long double __polevll(long double, const long double *, int);
 long double __p1evll(long double, const long double *, int);
 
-#if 0
-/* Attempt to get strict C99 semantics for assignment with non-C99 compilers. */
-#define STRICT_ASSIGN(type, lval, rval) do {    \
-        volatile type __v = (rval);             \
-        (lval) = __v;                           \
-} while (0)
-#else
-/* Should work with -fexcess-precision=standard (>=gcc-4.5) or -ffloat-store */
-#define STRICT_ASSIGN(type, lval, rval) ((lval) = (type)(rval))
-#endif
-
 #endif