Fix Armv8-M Baseline compilation

Armv8-M Baseline, ie thumbv8m.base-none-eabi, is a superset of the
Armv6-M architecture profile. As it shares almost the same instruction
set, this commit copies the configuration for thumbv6m-none-eabi to
enable it.

build.rs

@@ -49,10 +49,11 @@ fn main() {
         println!("cargo:rustc-cfg=thumb")
     }
 
-    // compiler-rt `cfg`s away some intrinsics for thumbv6m because that target doesn't have full
-    // THUMBv2 support. We have to cfg our code accordingly.
-    if llvm_target[0] == "thumbv6m" {
-        println!("cargo:rustc-cfg=thumbv6m")
+    // compiler-rt `cfg`s away some intrinsics for thumbv6m and thumbv8m.base because
+    // these targets do not have full Thumb-2 support but only original Thumb-1.
+    // We have to cfg our code accordingly.
+    if llvm_target[0] == "thumbv6m" || llvm_target[0] == "thumbv8m.base" {
+        println!("cargo:rustc-cfg=thumb_1")
     }
 
     // Only emit the ARM Linux atomic emulation on pre-ARMv6 architectures.
@@ -407,7 +408,7 @@ mod c {
         }
 
         // Remove the assembly implementations that won't compile for the target
-        if llvm_target[0] == "thumbv6m" {
+        if llvm_target[0] == "thumbv6m" || llvm_target[0] == "thumbv8m.base" {
             sources.remove(
                 &[
                     "clzdi2",

src/int/sdiv.rs

@@ -74,8 +74,8 @@ intrinsics! {
 
     #[use_c_shim_if(all(target_arch = "arm",
                     not(target_os = "ios"),
-                    not(target_env = "msvc")),
-                    not(thumbv6m))]
+                    not(target_env = "msvc"),
+                    not(thumb_1)))]
     pub extern "C" fn __modsi3(a: i32, b: i32) -> i32 {
         a.mod_(b)
     }
@@ -91,7 +91,7 @@ intrinsics! {
     }
 
     #[use_c_shim_if(all(target_arch = "arm", not(target_env = "msvc"),
-                    not(target_os = "ios"), not(thumbv6m)))]
+                    not(target_os = "ios"), not(thumb_1)))]
     pub extern "C" fn __divmodsi4(a: i32, b: i32, rem: &mut i32) -> i32 {
         a.divmod(b, rem, |a, b| __divsi3(a, b))
     }

src/int/udiv.rs

@@ -212,7 +212,7 @@ intrinsics! {
     #[use_c_shim_if(all(target_arch = "arm",
                         not(target_os = "ios"),
                         not(target_env = "msvc"),
-                        not(thumbv6m)))]
+                        not(thumb_1)))]
     /// Returns `n % d`
     pub extern "C" fn __umodsi3(n: u32, d: u32) -> u32 {
         let q = __udivsi3(n, d);
@@ -222,7 +222,7 @@ intrinsics! {
     #[use_c_shim_if(all(target_arch = "arm",
                         not(target_os = "ios"),
                         not(target_env = "msvc"),
-                        not(thumbv6m)))]
+                        not(thumb_1)))]
     /// Returns `n / d` and sets `*rem = n % d`
     pub extern "C" fn __udivmodsi4(n: u32, d: u32, rem: Option<&mut u32>) -> u32 {
         let q = __udivsi3(n, d);