[libc] Add ciel, frexpr implementations

The clang __builtin_* functions cannot be relied upon, as they may just
emit a call to the stdlib version. So this commit adds an implementation
for ceil and frexpr, as well as their float versions.

src/libraries/libc/math/frexpl.cpp

@@ -0,0 +1,4 @@
+#include <assert.h>
+
+extern "C"
+long double frexpl(long double f, int *exp) { assert(false && "NYI"); *exp = 0; return 0; }