rv32 rv64: adapt conditional compilation

Adapt conditional compilation as:
rv32i : riscv:__mulsi3, riscv:__muldi3
rv32im: riscv:__mulsi3, int/mul:__muldi3
rv64i : riscv:__mulsi3, riscv:__muldi3
rv64im: riscv:__mulsi3, int/mul:__muldi3

Author: johannst

src/int/mul.rs

@@ -100,7 +100,7 @@ impl_signed_mulo!(i128_overflowing_mul, i128, u128);
 intrinsics! {
     #[maybe_use_optimized_c_shim]
     #[arm_aeabi_alias = __aeabi_lmul]
-    #[cfg(not(target_arch = "riscv64"))]
+    #[cfg(any(not(any(target_arch = "riscv32", target_arch = "riscv64")), target_feature = "m"))]
     pub extern "C" fn __muldi3(a: u64, b: u64) -> u64 {
         a.mul(b)
     }

src/riscv.rs

@@ -1,7 +1,6 @@
 intrinsics! {
     // Implementation from gcc
     // https://raw.githubusercontent.com/gcc-mirror/gcc/master/libgcc/config/epiphany/mulsi3.c
-    #[cfg(target_arch = "riscv32")]
     pub extern "C" fn __mulsi3(a: u32, b: u32) -> u32 {
         let (mut a, mut b) = (a, b);
         let mut r = 0;
@@ -17,7 +16,7 @@ intrinsics! {
         r
     }
 
-    #[cfg(target_arch = "riscv64")]
+    #[cfg(not(target_feature = "m"))]
     pub extern "C" fn __muldi3(a: u64, b: u64) -> u64 {
         let (mut a, mut b) = (a, b);
         let mut r = 0;