Add a global elf cache.

Bug: 65682279

Test: Ran new unit tests.
Change-Id: I19c64614b2b11a27f58204d4cc34913c02e04c36
diff --git a/libunwindstack/Android.bp b/libunwindstack/Android.bp
index 8dae956..28d7e64 100644
--- a/libunwindstack/Android.bp
+++ b/libunwindstack/Android.bp
@@ -124,6 +124,7 @@
         "tests/DwarfOpTest.cpp",
         "tests/DwarfSectionTest.cpp",
         "tests/DwarfSectionImplTest.cpp",
+        "tests/ElfCacheTest.cpp",
         "tests/ElfFake.cpp",
         "tests/ElfInterfaceArmTest.cpp",
         "tests/ElfInterfaceTest.cpp",