[cmake] Do not set CMAKE_INCLUDE_CURRENT_DIR.

Setting this value is equivalent to setting:

include_directories(${CMAKE_CURRENT_BINARY_DIR} ${CMAKE_CURRENT_SOURCE_DIR})

in all subdirectories. Since these are all macros, this means that we are adding to the configuration
path the root swift directory. There is no reason to do this and will result in
confusion/bugs in the future.

rdar://26154980

Author: gottesmm

cmake/modules/SwiftSharedCMakeConfig.cmake

@@ -84,7 +84,6 @@ macro(swift_common_standalone_build_config_llvm 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(CMAKE_INCLUDE_CURRENT_DIR ON)
   include_directories("${PATH_TO_LLVM_BUILD}/include"
                       "${LLVM_MAIN_INCLUDE_DIR}")
   foreach (INCLUDE_DIR ${LLVM_INCLUDE_DIRS})

lib/ClangImporter/CMakeLists.txt

@@ -23,5 +23,7 @@ add_swift_library(swiftClangImporter STATIC
     swiftParse
 )
 
+# Include the current binary dir since we rely on gybed files.
+include_directories(${CMAKE_CURRENT_BINARY_DIR})
 
 add_dependencies(swiftClangImporter "${generated_include_targets}")

tools/SourceKit/tools/sourcekitd-test/CMakeLists.txt

@@ -1,6 +1,9 @@
 set(LLVM_TARGET_DEFINITIONS Options.td)
 swift_tablegen(Options.inc -gen-opt-parser-defs)
 swift_add_public_tablegen_target(sourcekitdTestOptionsTableGen)
+# Add this directories binary directory to the include list to make sure that we
+# can properly include Options.inc.
+include_directories(${CMAKE_CURRENT_BINARY_DIR})
 
 if(SWIFT_SOURCEKIT_USE_INPROC_LIBRARY)
   set(SOURCEKITD_TEST_DEPEND sourcekitdInProc)