[cmake] Remove dead set (i.e. LLVM_MAIN_INCLUDE_DIR already equals LLVM_MAIN_SRC_DIR/include).

rdar://26154980

Author: gottesmm

cmake/modules/SwiftSharedCMakeConfig.cmake

@@ -228,7 +228,6 @@ macro(swift_common_standalone_build_config product is_cross_compiling)
     "${PACKAGE_VERSION_MAJOR}.${PACKAGE_VERSION_MINOR}" CACHE STRING
     "Version number that will be placed into the libclang library , in the form XX.YY")
 
-  set(LLVM_MAIN_INCLUDE_DIR "${LLVM_MAIN_SRC_DIR}/include")
   set(CLANG_MAIN_INCLUDE_DIR "${CLANG_MAIN_SRC_DIR}/include")
   set(CMARK_MAIN_INCLUDE_DIR "${CMARK_MAIN_SRC_DIR}/src")
   set(CMARK_BUILD_INCLUDE_DIR "${PATH_TO_CMARK_BUILD}/src")