[compiler-rt][Android] Use correct builtins library name for tests

[rprichard]

Summary

The builtins library name is special on Android:

• There is an "-android" suffix.
• For the compiler-rt i386 architecture, Android targets i686 (in the triple and in the builtins library filename)

With this change, check-builtins works with Android.

[rprichard]

FWIW, to run check-builtins, I followed the instructions at https://llvm.org/docs/HowToCrossCompileBuiltinsOnArm.html, but adjusted them to use the NDK to build compiler-rt. Each test is a simple dynamic executable built with something like -nodefaultlibs -lc -lm, and I set -DCOMPILER_RT_EMULATOR to a script I have that runs a program using adb push and adb shell.

To run the tests on arm32, I also needed to make this change, D82147. Some of the floating-point tests also failed, and were fixed by my other 80-bit FP revisions.

compiler-rt/test/lit.common.configured.in

 set_default("android_files_to_push", [])
 set_default("have_rpc_xdr_h", @HAVE_RPC_XDR_H@)
 set_default("gwp_asan", @COMPILER_RT_HAS_GWP_ASAN_PYBOOL@)
 set_default("expensive_checks", @LLVM_ENABLE_EXPENSIVE_CHECKS_PYBOOL@)
 config.available_features.add('target-is-%s' % config.target_arch)
 
 if config.enable_per_target_runtime_dir:
   set_default("target_suffix", "")
+elif config.android:
+  if config.target_arch == "i386":
+    set_default("target_suffix", "-i686-android")
+  else:
+    set_default("target_suffix", "-%s-android" % config.target_arch)
 else:
   set_default("target_suffix", "-%s" % config.target_arch)
 
 set_default("have_zlib", "@HAVE_LIBZ@")
 set_default("libcxx_used", "@LLVM_LIBCXX_USED@")
 
 # LLVM tools dir can be passed in lit parameters, so try to
 # apply substitution.