Add prebuilt ELF binaries checker

This commit introduces a prebuilt ELF binaries checker.  The checker
will check:

1. Whether all DT_NEEDED shared libraries are specified in
   `shared_libs` (Android.bp) or `LOCAL_SHARED_LIBRARIES` (Android.mk).

2. Whether all undefined symbols in the prebuilt binary can be resolved
   to defined symbols exported by its dependencies.

This ensures that prebuilt binaries won't silently become ABI
incompatible.

To check the prebuilt binaries, all of the dependencies must be
specified in `shared_libs` (Android.bp) or `LOCAL_SHARED_LIBRARIES`
(Android.mk).

If your prebuilt binaries cannot be checked for some reason, you may add
the following property to Android.bp:

    check_elf_files: false,

Or, add the following setting to Android.mk:

    LOCAL_CHECK_ELF_FILES := false

Bug: 119084334
Test: CHECK_ELF_FILES=true make check-elf-files
Change-Id: I523d3083f22fd4053c096d26f61f8375800281c8
diff --git a/core/clang/config.mk b/core/clang/config.mk
index ca3a1fa..063fd34 100644
--- a/core/clang/config.mk
+++ b/core/clang/config.mk
@@ -1,5 +1,7 @@
 ## Clang configurations.
 
+LLVM_READOBJ := $(LLVM_PREBUILTS_BASE)/$(BUILD_OS)-x86/$(LLVM_PREBUILTS_VERSION)/bin/llvm-readobj
+
 LLVM_RTLIB_PATH := $(LLVM_PREBUILTS_BASE)/linux-x86/$(LLVM_PREBUILTS_VERSION)/lib64/clang/$(LLVM_RELEASE_VERSION)/lib/linux/
 
 define convert-to-clang-flags