[PATCH] Constant folding pow(x,y) for constant y.

[David Edelsohn]

	I just tried to bootstrap and received the following error:

/gcc/dje/src/gcc/builtins.c: In function `fold_builtin':
/gcc/dje/src/gcc/builtins.c:4881: `dconstm2' undeclared (first use in this funct
ion)
/gcc/dje/src/gcc/builtins.c:4881: (Each undeclared identifier is reported only o
nce
/gcc/dje/src/gcc/builtins.c:4881: for each function it appears in.)
/gcc/dje/src/gcc/builtins.c:4894: `dconsthalf' undeclared (first use in this fun
ction)
make[2]: *** [builtins.o] Error 1