games/libretro-beetle_psx: Fix build on armv7

The functions addsf3 and adddf3 are part of libgcc which is not
provided when compiling with clang. Fiddle with some #if directives to
provide shims if we compile with clang.

PR: 268077
MFH: 2022Q4 (build fix)
(cherry picked from commit 4b93307b9d1762c72e68c229301795c8ebdc79fc)