[CMake] Properly conditionalize installation of lld libraries

In what appears to be a copy-and-paste error, lld currently only
installs libraries if the lld tools are configured to build.

Instead, lld should allow the libraries to be installed even if the lld
tools are not being built. Additionally, if users want to only install
the tools and not the libraries, the LLVM way of doing that is by
checking for LLVM_INSTALL_TOOLCHAIN_ONLY.

This fixes PR35960.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@327126 91177308-0d34-0410-b5e6-96231b3b80d8

Author: davezarzycki

cmake/modules/AddLLD.cmake

@@ -10,7 +10,7 @@ macro(add_lld_library name)
   llvm_add_library(${name} ${ARG_ENABLE_SHARED} ${ARG_UNPARSED_ARGUMENTS})
   set_target_properties(${name} PROPERTIES FOLDER "lld libraries")
 
-  if (LLD_BUILD_TOOLS)
+  if (NOT LLVM_INSTALL_TOOLCHAIN_ONLY)
     if(${name} IN_LIST LLVM_DISTRIBUTION_COMPONENTS OR
         NOT LLVM_DISTRIBUTION_COMPONENTS)
       set(export_to_lldtargets EXPORT lldTargets)