fix(cmake): add CMAKE_INSTALL_LIBDIR for ext_gtest to fix lib64 path on aarch64 (#34793)

On CentOS 7 aarch64, GNUInstallDirs defaults to lib64, causing ext_gtest
to install libraries to lib64/ while CMake expects lib/. This is consistent
with how other ExternalProject targets already handle this (e.g. ext_libuv,
ext_snappy, ext_rocksdb, etc.).

Author: boxiaobj

cmake/external.cmake

@@ -389,6 +389,7 @@ if(${BUILD_TEST})           # {
         PREFIX "${_base}"
         CMAKE_ARGS -DCMAKE_BUILD_TYPE:STRING=${TD_CONFIG_NAME}
         CMAKE_ARGS -DCMAKE_INSTALL_PREFIX:STRING=${_ins}
+        CMAKE_ARGS -DCMAKE_INSTALL_LIBDIR:PATH=lib
         CMAKE_ARGS -Dgtest_force_shared_crt:BOOL=ON
         BUILD_COMMAND
             COMMAND "${CMAKE_COMMAND}" --build . --config "${TD_CONFIG_NAME}"