Use llvm-{objcopy,strip} when clang lld is used.

* Pass LLVM_{OBJCOPY,STRIP} to makefile rules.
* strip.sh is used only in soong-only mode.
  It will use llvm-strip and  and llvm-objcopy
  when --use-llvm-strip is given.
  Keep flags of strip.sh in alphabetic order.
* Tested build/soong/scripts/build-ndk-prebuilts.sh
  by adding "UseClangLld": true, to soong.variables file.

Bug: 80093681
Test: build/soong/scripts/build-ndk-prebuilts.sh
Change-Id: I612267304eea434c7a33cc086b27b577d5f64094
diff --git a/cc/makevars.go b/cc/makevars.go
index d036bb6..8b72dbb 100644
--- a/cc/makevars.go
+++ b/cc/makevars.go
@@ -72,6 +72,8 @@
 	ctx.Strict("CLANG_CXX", "${config.ClangBin}/clang++")
 	ctx.Strict("LLVM_AS", "${config.ClangBin}/llvm-as")
 	ctx.Strict("LLVM_LINK", "${config.ClangBin}/llvm-link")
+	ctx.Strict("LLVM_OBJCOPY", "${config.ClangBin}/llvm-objcopy")
+	ctx.Strict("LLVM_STRIP", "${config.ClangBin}/llvm-strip")
 	ctx.Strict("PATH_TO_CLANG_TIDY", "${config.ClangBin}/clang-tidy")
 	ctx.StrictSorted("CLANG_CONFIG_UNKNOWN_CFLAGS", strings.Join(config.ClangUnknownCflags, " "))