[Fuzzer] Enable custom libc++ for Android (#70407)

The Android LLVM build system builds the arm64 fuzzer lib without
HWASan, but then applications that enable HWASan can generated an object
file with a HWASan-ified version of some libc++ symbols (e.g.
`std::__1::piecewise_construct`). The linker can choose the HWASan-ified
definition, but then it cannot resolve the relocation from
libclang_rt.fuzzer-aarch64-android.a to this symbol because the high
bits of the address are unexpectedly set. This produces an error:

```
relocation R_AARCH64_ADR_PREL_PG_HI21 out of range
```

Fix this problem by linking a custom isolated libc++ into Android's
fuzzer library.

We need to pass through ANDROID_NATIVE_API_LEVEL so that the libc++ for
32-bit Android (API < 24) uses LLVM_FORCE_SMALLFILE_FOR_ANDROID.

Author: rprichard

compiler-rt/cmake/Modules/AddCompilerRT.cmake

@@ -625,6 +625,8 @@ macro(add_custom_libcxx name prefix)
   set_target_properties(${name}-clobber PROPERTIES FOLDER "Compiler-RT Misc")
 
   set(PASSTHROUGH_VARIABLES
+    ANDROID
+    ANDROID_NATIVE_API_LEVEL
     CMAKE_C_COMPILER_TARGET
     CMAKE_CXX_COMPILER_TARGET
     CMAKE_SHARED_LINKER_FLAGS

compiler-rt/lib/fuzzer/CMakeLists.txt

@@ -59,7 +59,7 @@ CHECK_CXX_SOURCE_COMPILES("
 
 set(LIBFUZZER_CFLAGS ${COMPILER_RT_COMMON_CFLAGS})
 
-if(OS_NAME MATCHES "Linux|Fuchsia" AND
+if(OS_NAME MATCHES "Android|Linux|Fuchsia" AND
    COMPILER_RT_LIBCXX_PATH AND
    COMPILER_RT_LIBCXXABI_PATH)
   list(APPEND LIBFUZZER_CFLAGS -D_LIBCPP_ABI_VERSION=Fuzzer)
@@ -135,7 +135,7 @@ add_compiler_rt_runtime(clang_rt.fuzzer_interceptors
   CFLAGS ${LIBFUZZER_CFLAGS}
   PARENT_TARGET fuzzer)
 
-if(OS_NAME MATCHES "Linux|Fuchsia" AND
+if(OS_NAME MATCHES "Android|Linux|Fuchsia" AND
    COMPILER_RT_LIBCXX_PATH AND
    COMPILER_RT_LIBCXXABI_PATH)
   macro(partially_link_libcxx name dir arch)