Sync math operator/utility functions from pokeheartgold

Compared/synced by hand from the pokeheartgold asm.

Some of the functions had labels corresponding to libgcc counterparts;
rename them all for consistency.

Note that some of the functions have multiple names in pokeheartgold
(of which at most one is actually used). Instead of polluting the xMAP
files with multiple symbols (some with zero length), which makes it
really hard for scripts to parse, just add these alternate names as
comments. This makes them searchable without having an effect on build
artifacts.

lib/asm/include/crt0.inc

@@ -7,5 +7,5 @@
 .public SDK_STATIC_BSS_END
 .public SDK_STATIC_BSS_START
 .public sub_01FF95E8
-.public sub_020907F0
+.public _fp_init
 .public sub_020908A8