Bug 1674180 - Use the llvm-readobj from the build instead of the NDK. r=nalexander

The llvm-readobj in the NDK is not part of the same toolchain that is used to
build Gecko, and in some cases this difference causes the build to fail (e.g.
local ASAN builds trip into this).

To fix this we use the llvm-readobj from the clang directory, when available.

Differential Revision: https://phabricator.services.mozilla.com/D104117

mobile/android/gradle/with_gecko_binaries.gradle

@@ -13,12 +13,11 @@ import java.nio.file.Path
 import java.nio.file.Paths
 import java.security.MessageDigest
 
-// To find the LLVM tools from the Android NDK, there are a few wrinkles.  In a compiled build,
-// we can use our own `ANDROID_NDK` configure option.  But in an artifact build, that isn't
-// defined, so we fall back to `android.ndkDirectory` -- but that's defined in
-// `local.properties`, which may not define it.  In that case, fall back to crawling the
-// filesystem.
-@Memoized
+// To find the Android NDK directory, there are a few wrinkles.  In a compiled
+// build, we can use our own `ANDROID_NDK` configure option.  But in an
+// artifact build, that isn't defined, so we fall back to
+// `android.ndkDirectory` -- but that's defined in `local.properties`, which
+// may not define it.  In that case, fall back to crawling the filesystem.
 def getNDKDirectory() {
     if (project.mozconfig.substs.ANDROID_NDK) {
         return project.mozconfig.substs.ANDROID_NDK
@@ -35,9 +34,35 @@ def getNDKDirectory() {
     return null
 }
 
-ext.getNDKDirectory = {
+// Get the LLVM bin folder, either from the currently used toolchain or, if
+// this is an artifact build, from the Android NDK.
+@Memoized
+def getLlvmBinFolder() {
+    // If we have a clang path, just use that
+    if (project.mozconfig.substs.MOZ_CLANG_PATH) {
+        return project.file(project.mozconfig.substs.MOZ_CLANG_PATH)
+            .parentFile
+    }
+
+    def ndkDirectory = getNDKDirectory()
+    if (!ndkDirectory) {
+        // Give up
+        return null;
+    }
+
+    // The `**` in the pattern depends on the host architecture.  We could compute them or bake them
+    // in, but this is easy enough.  `FileNameFinder` won't return a directory, so we find a file
+    // and return its parent directory.
+    return project
+        .file(new FileNameFinder()
+                  .getFileNames(ndkDirectory, "toolchains/llvm/prebuilt/**/bin/llvm-*")
+                  .first())
+        .parentFile
+}
+
+ext.getLlvmBinFolder = {
     // This is the easiest way to expose the memoized function to consumers.
-    getNDKDirectory()
+    getLlvmBinFolder()
 }
 
 // Bug 1657190: This task works around a bug in the Android-Gradle plugin.  When using SNAPSHOT
@@ -64,12 +89,8 @@ class SyncLibsAndUpdateGenerationID extends DefaultTask {
     @OutputDirectory
     File destinationDir
 
-    // The `**` in the pattern depends on the host architecture.  We could compute them or bake them
-    // in, but this is easy enough.  `FileNameFinder` won't return a directory, so we find a file
-    // and return its parent directory.
     @Input
-    File llvmBin = project.file(new FileNameFinder().getFileNames(project.ext.getNDKDirectory(), "toolchains/llvm/prebuilt/**/bin/llvm-*")
-                                .first()).parentFile
+    File llvmBin = project.ext.getLlvmBinFolder()
 
     // Sibling to `.note.gnu.build-id`.
     @Input
@@ -191,8 +212,8 @@ ext.configureVariantWithGeckoBinaries = { variant ->
             return false
         } else if (mozconfig.substs.MOZ_ANDROID_FAT_AAR_ARCHITECTURES) {
             return false
-        } else if (ext.getNDKDirectory() == null) {
-            logger.warn("Could not determine Android NDK directory.")
+        } else if (ext.getLlvmBinFolder() == null) {
+            logger.warn("Could not determine LLVM bin directory.")
             logger.warn("Set `ndk.dir` in `${project.topsrcdir}/local.properties` to avoid startup crashes when using `substitute-local-geckoview.gradle`.")
             logger.warn("See https://bugzilla.mozilla.org/show_bug.cgi?id=1657190.")
             return false