Add support for llvm-mc as an assembly linter (#4446)

doc/ale-asm.txt

@@ -21,5 +21,24 @@ g:ale_asm_gcc_options                                   *g:ale_asm_gcc_options*
   This variable can be set to pass additional options to gcc.
 
 
+===============================================================================
+llvm_mc                                                       *ale-asm-llvm_mc*
+
+g:ale_asm_clang_executable                       *g:ale_asm_llvm_mc_executable*
+                                                 *b:ale_asm_llvm_mc_executable*
+  Type: |String|
+  Default: `'llvm-mc'`
+
+This variable can be changed to use a different executable for llvm-mc.
+
+
+g:ale_asm_clang_options                             *g:ale_asm_llvm_mc_options*
+                                                    *b:ale_asm_llvm_mc_options*
+  Type: |String|
+  Default: `''`
+
+  This variable can be set to pass additional options to llvm-mc.
+
+
 ===============================================================================
   vim:tw=78:ts=2:sts=2:sw=2:ft=help:norl:

doc/ale-supported-languages-and-tools.txt

@@ -36,6 +36,7 @@ Notes:
   * `write-good`
 * ASM
   * `gcc`
+  * `llvm-mc`
 * AVRA
   * `avra`
 * Awk

doc/ale.txt

@@ -2809,6 +2809,7 @@ documented in additional help files.
     textlint..............................|ale-asciidoc-textlint|
   asm.....................................|ale-asm-options|
     gcc...................................|ale-asm-gcc|
+    llvm_mc...............................|ale-asm-llvm_mc|
   avra....................................|ale-avra-options|
     avra..................................|ale-avra-avra|
   awk.....................................|ale-awk-options|