Revert "[libcxx] Force-cache LIBCXX_CXX_ABI_LIBRARY_PATH"

This reverts commit 41f4dfd63ea0fe995ddfba1838aa5ed972cc1377.

It broke standalone libc++ builds, which now try to use libc++abi from the wrong directory, instead of system instance.

(cherry picked from commit 3573526c0286c9461f0459be1a4592b2214594e7)

Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 1a7e688b0b5a986fbbbce62ff1506a5991b0fce0
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 6dd8fb6..8147451 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -46,7 +46,7 @@
 # directory.
 if (NOT LIBCXX_CXX_ABI_LIBRARY_PATH)
   set(LIBCXX_CXX_ABI_LIBRARY_PATH "${LIBCXX_LIBRARY_DIR}" CACHE PATH
-      "The path to libc++abi library." FORCE)
+      "The path to libc++abi library.")
 endif()
 
 set(LIBCXX_TARGET_INFO "libcxx.test.target_info.LocalTI" CACHE STRING