[cmake] Instead of setting LLVM_TABLEGEN_EXE, use our own SWIFT_TABLEGEN_EXE variable.

This eliminates us setting an LLVM_ prefixed variable in a situation where there is
a viable alternative.

We want to eliminate as many of these as possible since they can cause conflicts
with variables set in LLVMConfig.cmake.

I also added some convenience tablegen functions in AddSwiftTableGen.cmake and
changed all tblgen users to use that instead.

rdar://26154980

Author: gottesmm

cmake/modules/AddSwiftTableGen.cmake

@@ -0,0 +1,13 @@
+include(TableGen)
+
+# This needs to be a macro since tablegen (which is a function) needs to set
+# variables in its parent scope.
+macro(swift_tablegen)
+  tablegen(SWIFT ${ARGN})
+endmacro()
+
+# This needs to be a macro since add_public_tablegen_target (which is a
+# function) needs to set variables in its parent scope.
+macro(swift_add_public_tablegen_target target)
+  add_public_tablegen_target(${target})
+endmacro()

cmake/modules/SwiftSharedCMakeConfig.cmake

@@ -109,19 +109,19 @@ macro(swift_common_standalone_build_config product is_cross_compiling)
   list(APPEND CMAKE_MODULE_PATH "${${product}_PATH_TO_LLVM_BUILD}/share/llvm/cmake")
 
   if(${is_cross_compiling})
-    find_program(LLVM_TABLEGEN_EXE "llvm-tblgen" "${${product}_NATIVE_LLVM_TOOLS_PATH}"
+    find_program(SWIFT_TABLEGEN_EXE "llvm-tblgen" "${${product}_NATIVE_LLVM_TOOLS_PATH}"
       NO_DEFAULT_PATH)
-    if ("${LLVM_TABLEGEN_EXE}" STREQUAL "LLVM_TABLEGEN_EXE-NOTFOUND")
+    if ("${SWIFT_TABLEGEN_EXE}" STREQUAL "SWIFT_TABLEGEN_EXE-NOTFOUND")
       message(FATAL_ERROR "Failed to find tablegen in ${${product}_NATIVE_LLVM_TOOLS_PATH}")
     endif()
   else()
-    set(LLVM_TABLEGEN_EXE llvm-tblgen)
+    set(SWIFT_TABLEGEN_EXE llvm-tblgen)
     set(${product}_NATIVE_LLVM_TOOLS_PATH "${PATH_TO_LLVM_TOOLS_BINARY_DIR}")
     set(${product}_NATIVE_CLANG_TOOLS_PATH "${PATH_TO_LLVM_TOOLS_BINARY_DIR}")
   endif()
 
   include(AddLLVM)
-  include(TableGen)
+  include(AddSwiftTableGen) # This imports TableGen from LLVM.
   include(HandleLLVMOptions)
 
   set(PACKAGE_VERSION "${LLVM_PACKAGE_VERSION}")

include/swift/Option/CMakeLists.txt

@@ -1,3 +1,3 @@
 set(LLVM_TARGET_DEFINITIONS Options.td)
-tablegen(LLVM Options.inc -gen-opt-parser-defs)
-add_public_tablegen_target(SwiftOptions)
+swift_tablegen(Options.inc -gen-opt-parser-defs)
+swift_add_public_tablegen_target(SwiftOptions)

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

@@ -1,6 +1,6 @@
 set(LLVM_TARGET_DEFINITIONS Options.td)
-tablegen(LLVM Options.inc -gen-opt-parser-defs)
-add_public_tablegen_target(sourcekitdTestOptionsTableGen)
+swift_tablegen(Options.inc -gen-opt-parser-defs)
+swift_add_public_tablegen_target(sourcekitdTestOptionsTableGen)
 
 if(SWIFT_SOURCEKIT_USE_INPROC_LIBRARY)
   set(SOURCEKITD_TEST_DEPEND sourcekitdInProc)