[clangd] Forward all environment variables along with CLANGD_TRACE to clangd.
[clangd] Forward all environment variables along with CLANGD_TRACE to clangd.

git-svn-id: a34e9779ed74578ad5922b3306b3d80a0c825546@326452 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/clang-tools-extra,llvm-mirror/clang-tools-extra,llvm-mirror/clang-tools-extra,llvm-mirror/clang-tools-extra