bp2build: export some cc toolchain flags into Starlark.

This CL exports common/global/device/host clang/ld/ldd flags
from their Ninja variable initialization locations in
cc/config/global.go and cc/config/clang.go to make Bazel's cc_toolchain
and Soong's cc actions more consistent with each other.

This does not handle env-dependent or arch-specific toolchain flags
yet (logic in compiler.go and linker.go).

Test: TH
Bug: 187086342
Bug: 187084737
Bug: 186628704
Bug: 187857770
Change-Id: Ie403d7cd23f35160897b9dd902c799cbf1bd7f0c
diff --git a/cc/config/Android.bp b/cc/config/Android.bp
index 5ef247d..e4a8b62 100644
--- a/cc/config/Android.bp
+++ b/cc/config/Android.bp
@@ -10,6 +10,7 @@
         "soong-remoteexec",
     ],
     srcs: [
+        "bp2build.go",
         "clang.go",
         "global.go",
         "tidy.go",
@@ -31,6 +32,7 @@
         "arm64_linux_host.go",
     ],
     testSrcs: [
+        "bp2build_test.go",
         "tidy_test.go",
     ],
 }