Support grouping static libraries

LLVM has complicated static library layering that sometimes changes.
The make solution was to list all the static libraries twice, but
Soong dedups the list.  Add a group_static_libs flag to allow
surrounding the static libs with -Wl,--start-group and
-Wl,--end-group.

Test: mmma -j external/llvm
Change-Id: Ic08a183d7def9c9249d4a3014760759f16b68d04

cc/builder.go

@@ -187,6 +187,8 @@ type builderFlags struct {
 	clang       bool
 	tidy        bool
 
+	groupStaticLibs bool
+
 	stripKeepSymbols       bool
 	stripKeepMiniDebugInfo bool
 	stripAddGnuDebuglink   bool
@@ -439,7 +441,13 @@ func TransformObjToDynamicBinary(ctx android.ModuleContext,
 		}
 	}
 
+	if flags.groupStaticLibs && len(staticLibs) > 0 {
+		libFlagsList = append(libFlagsList, "-Wl,--start-group")
+	}
 	libFlagsList = append(libFlagsList, staticLibs.Strings()...)
+	if flags.groupStaticLibs && len(staticLibs) > 0 {
+		libFlagsList = append(libFlagsList, "-Wl,--end-group")
+	}
 
 	if groupLate && !ctx.Darwin() && len(lateStaticLibs) > 0 {
 		libFlagsList = append(libFlagsList, "-Wl,--start-group")