[scripts] Remove hard-coded clang version

Bug: http://b/187231324

Instead,
- For local development, invoke build/soong/scripts/get_clang_version.py
to find the current clang version.
- In CI, find llvm-cxxfilt using glob expansion.

Test: development/scripts/symbol.py unittest for local development
      python-stack_core_test on presubmit
Change-Id: Id4258dd791626508520b6a478b8a1b54495ebb11

scripts/symbol.py

@@ -31,6 +31,18 @@ import unittest
 
 ANDROID_BUILD_TOP = os.environ.get("ANDROID_BUILD_TOP", ".")
 
+
+def FindClangDir():
+  get_clang_version = ANDROID_BUILD_TOP + "/build/soong/scripts/get_clang_version.py"
+  if os.path.exists(get_clang_version):
+    # We want the script to fail if get_clang_version.py exists but is unable
+    # to find the clang version.
+    version_output = subprocess.check_output(get_clang_version, text=True)
+    return ANDROID_BUILD_TOP + "/prebuilts/clang/host/linux-x86/" + version_output.strip()
+  else:
+    return None
+
+
 def FindSymbolsDir():
   saveddir = os.getcwd()
   os.chdir(ANDROID_BUILD_TOP)
@@ -437,9 +449,19 @@ def CallCppFilt(mangled_symbol):
   global _CACHED_CXX_FILT
   if not _CACHED_CXX_FILT:
     toolchains = None
-    # TODO(b/187231324) do not hard-code prebuilt version number below
-    if os.path.exists('./clang-r416183b1/bin/llvm-cxxfilt'):
-      toolchains = ["./clang-r416183b1/bin/llvm-cxxfilt"]
+    clang_dir = FindClangDir()
+    if clang_dir:
+      if os.path.exists(clang_dir + "/bin/llvm-cxxfilt"):
+        toolchains = [clang_dir + "/bin/llvm-cxxfilt"]
+      else:
+        raise Exception("bin/llvm-cxxfilt missing from " + clang_dir)
+    else:
+      # When run in CI, we don't have a way to find the clang version.  But
+      # llvm-cxxfilt should be available in the following relative path.
+      toolchains = glob.glob("./clang-r*/bin/llvm-cxxfilt")
+      if toolchains and len(toolchains) != 1:
+        raise Exception("Expected one llvm-cxxfilt but found many: " + \
+                        ", ".join(toolchains))
     if not toolchains:
       raise Exception("Could not find llvm-cxxfilt tool")
     _CACHED_CXX_FILT = sorted(toolchains)[-1]
@@ -550,6 +572,11 @@ class FindToolchainTests(unittest.TestCase):
     self.assert_toolchain_found("x86")
     self.assert_toolchain_found("x86_64")
 
+class FindClangDirTests(unittest.TestCase):
+  @unittest.skipIf(ANDROID_BUILD_TOP == '.', 'Test only supported in an Android tree.')
+  def test_clang_dir_found(self):
+    self.assertIsNotNone(FindClangDir())
+
 class SetArchTests(unittest.TestCase):
   def test_abi_check(self):
     global ARCH