Add a safe wrapper for LLVMAppendModuleInlineAsm

This patch also changes the Rust-side declaration to take `*const c_uchar`
instead of `*const c_char`, to avoid the need for `AsCCharPtr`.

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -1014,8 +1014,12 @@ unsafe extern "C" {
     pub(crate) fn LLVMGetDataLayoutStr(M: &Module) -> *const c_char;
     pub(crate) fn LLVMSetDataLayout(M: &Module, Triple: *const c_char);
 
-    /// See Module::setModuleInlineAsm.
-    pub(crate) fn LLVMAppendModuleInlineAsm(M: &Module, Asm: *const c_char, Len: size_t);
+    /// Append inline assembly to a module. See `Module::appendModuleInlineAsm`.
+    pub(crate) fn LLVMAppendModuleInlineAsm(
+        M: &Module,
+        Asm: *const c_uchar, // See "PTR_LEN_STR".
+        Len: size_t,
+    );
 
     /// Create the specified uniqued inline asm string. See `InlineAsm::get()`.
     pub(crate) fn LLVMGetInlineAsm<'ll>(

compiler/rustc_codegen_llvm/src/llvm/mod.rs

@@ -440,3 +440,11 @@ pub(crate) fn set_dso_local<'ll>(v: &'ll Value) {
         LLVMRustSetDSOLocal(v, true);
     }
 }
+
+/// Safe wrapper for `LLVMAppendModuleInlineAsm`, which delegates to
+/// `Module::appendModuleInlineAsm`.
+pub(crate) fn append_module_inline_asm<'ll>(llmod: &'ll Module, asm: &[u8]) {
+    unsafe {
+        LLVMAppendModuleInlineAsm(llmod, asm.as_ptr(), asm.len());
+    }
+}