Enable math module for riscv32 targets

This is likely a bug fix since in math.rs there are already
config attributes that are mentioning this target

Author: mchodzikiewicz

src/lib.rs

@@ -48,6 +48,7 @@ pub mod int;
     all(target_arch = "x86_64", target_os = "none"),
     all(target_arch = "x86_64", target_os = "uefi"),
     all(target_arch = "arm", target_os = "none"),
+    all(target_arch = "riscv32", target_os = "none"),
     all(target_arch = "xtensa", target_os = "none"),
     all(target_arch = "mips", target_os = "none"),
     target_os = "xous",