[cmake] fix a typo in llvm_config macro

[labath]

Summary

The macro parses out the USE_SHARED option out of the argument list, but
then ignores it and accesses the variable with the same name instead. It
seems the intention here was to check the argument value.

Technically, this is NFC, because the only in-tree usage
(add_llvm_executable) of USE_SHARED sets both the variable and the
argument when calling llvm_config, but it makes the usage of this macro
for out-of-tree users more sensible.

[foutrelis]

+1 from me; it fixes llvm_config(foo USE_SHARED ...) for out-of-tree builds.

[mgorny]

Good catch! LGTM.

That said, I wonder if this works with split shared libraries. But if not, that's a separate bug to address, so shouldn't really block this.

[labath]

In D44420#1123236, @mgorny wrote:

Good catch! LGTM.

That said, I wonder if this works with split shared libraries. But if not, that's a separate bug to address, so shouldn't really block this.

IIRC, I too got the impression that this wasn't doing the right thing for BUILD_SHARED_LIBS, though I don't remember what was the reason.

llvm/trunk/cmake/modules/LLVM-Config.cmake

if(NOT ${return_var})
     endif()
   endif()
 endfunction()
 
 macro(llvm_config executable)
   cmake_parse_arguments(ARG "USE_SHARED" "" "" ${ARGN})
   set(link_components ${ARG_UNPARSED_ARGUMENTS})
 
-  if(USE_SHARED)
+  if(ARG_USE_SHARED)
     # If USE_SHARED is specified, then we link against libLLVM,
     # but also against the component libraries below. This is
     # done in case libLLVM does not contain all of the components
     # the target requires.
     #
     # Strip LLVM_DYLIB_COMPONENTS out of link_components.
     # To do this, we need special handling for "all", since that
     # may imply linking to libraries that are not included in