test runner: Replace all_modules with MODULES-IN-*

all_modules would trigger all Soong modules to be built and installed.

Bug: 30191725
Test: Ran external/libcxx/run-tests.py, appears to build properly
Change-Id: I11ff39c5681c4b07b8b6456b7302531e4e746e15

test/libcxx/android/build.py

@@ -8,6 +8,6 @@ def mm(path, android_build_top):
 
     cmd = [
         'make', '-C', android_build_top, '-f', 'build/core/main.mk',
-        'all_modules', '-B'
+        'MODULES-IN-' + path.replace('/', '-'), '-B'
     ]
     return not subprocess.Popen(cmd, stdout=None, stderr=None, env=env).wait()