Pass llvm opts when compiling .ll files. (#15486)

I broke this in #12705 when I started treating `.ll` files like `.s`
files and not passing any c flags (or llvm flags).

Fixes: #15370

Author: sbc100

emcc.py

@@ -60,16 +60,15 @@
 CXX_ENDINGS = ('.cpp', '.cxx', '.cc', '.c++', '.CPP', '.CXX', '.C', '.CC', '.C++', '.ii')
 OBJC_ENDINGS = ('.m', '.mi')
 OBJCXX_ENDINGS = ('.mm', '.mii')
-ASSEMBLY_CPP_ENDINGS = ('.S',)
 SPECIAL_ENDINGLESS_FILENAMES = (os.devnull,)
 
-SOURCE_ENDINGS = C_ENDINGS + CXX_ENDINGS + OBJC_ENDINGS + OBJCXX_ENDINGS + SPECIAL_ENDINGLESS_FILENAMES + ASSEMBLY_CPP_ENDINGS
+SOURCE_ENDINGS = C_ENDINGS + CXX_ENDINGS + OBJC_ENDINGS + OBJCXX_ENDINGS + SPECIAL_ENDINGLESS_FILENAMES + ('.ll', '.S')
 C_ENDINGS = C_ENDINGS + SPECIAL_ENDINGLESS_FILENAMES # consider the special endingless filenames like /dev/null to be C
 
 EXECUTABLE_ENDINGS = ('.wasm', '.html', '.js', '.mjs', '.out', '')
 DYNAMICLIB_ENDINGS = ('.dylib', '.so') # Windows .dll suffix is not included in this list, since those are never linked to directly on the command line.
 STATICLIB_ENDINGS = ('.a',)
-ASSEMBLY_ENDINGS = ('.ll', '.s')
+ASSEMBLY_ENDINGS = ('.s',)
 HEADER_ENDINGS = ('.h', '.hxx', '.hpp', '.hh', '.H', '.HXX', '.HPP', '.HH')
 
 # Supported LLD flags which we will pass through to the linker.

tests/test_other.py

@@ -4337,6 +4337,14 @@ def test_emit_llvm(self):
     self.run_process([EMCC, test_file('hello_world.c'), '-c', '-emit-llvm'])
     self.assertTrue(building.is_bitcode('hello_world.bc'))
 
+  def test_compile_ll_file(self):
+    self.run_process([EMCC, test_file('hello_world.c'), '-S', '-emit-llvm'])
+    err = self.run_process([EMCC, '-v', '-c', 'hello_world.ll', '-o', 'hello_world.o'], stderr=PIPE).stderr
+    # Verify that `-mllvm` flags are passed when compiling `.ll` files.
+    self.assertContained('-mllvm -enable-emscripten-sjlj', err)
+    self.run_process([EMCC, 'hello_world.o'])
+    self.assertContained('hello, world!', self.run_js('a.out.js'))
+
   def test_dashE(self):
     create_file('src.cpp', r'''#include <emscripten.h>
 __EMSCRIPTEN_major__ __EMSCRIPTEN_minor__ __EMSCRIPTEN_tiny__ EMSCRIPTEN_KEEPALIVE