[CMake] Create tool header collector target only when building tools

`HeaderDependencies.cpp` cannot be compiled with
`SWIFT_INCLUDE_TOOLS=OFF` because it depends on `Config.h` which is only
generated while building tools. Exclude it from the build to fix `all`
target.

Follow-up to b39dba3

Author: kateinoigakukun

include/CMakeLists.txt

@@ -1,30 +1,32 @@
 add_subdirectory(swift)
 
+if(SWIFT_INCLUDE_TOOLS)
 
-# Create a library that depends on all headers defined in include/swift/module.modulemap
-#
-# TODO: generate this dynamically through the modulemap; this cannot use `sed`
-# as that is not available on all platforms (e.g. Windows).
-file(GENERATE
-  OUTPUT "${CMAKE_CURRENT_BINARY_DIR}/HeaderDependencies.cpp"
-  CONTENT "
-#define COMPILED_WITH_SWIFT
-#define SWIFT_TARGET
+  # Create a library that depends on all tool headers defined in include/module.modulemap
+  #
+  # TODO: generate this dynamically through the modulemap; this cannot use `sed`
+  # as that is not available on all platforms (e.g. Windows).
+  file(GENERATE
+    OUTPUT "${CMAKE_CURRENT_BINARY_DIR}/HeaderDependencies.cpp"
+    CONTENT "
+  #define COMPILED_WITH_SWIFT
+  #define SWIFT_TARGET
 
-#include \"swift/Basic/BasicBridging.h\"
-#include \"swift/AST/ASTBridging.h\"
-#include \"swift/IDE/IDEBridging.h\"
-#include \"swift/Parse/ParseBridging.h\"
-#include \"swift/SIL/SILBridging.h\"
-#include \"swift/SILOptimizer/OptimizerBridging.h\"
-")
-add_library(importedHeaderDependencies "${CMAKE_CURRENT_BINARY_DIR}/HeaderDependencies.cpp")
+  #include \"swift/Basic/BasicBridging.h\"
+  #include \"swift/AST/ASTBridging.h\"
+  #include \"swift/IDE/IDEBridging.h\"
+  #include \"swift/Parse/ParseBridging.h\"
+  #include \"swift/SIL/SILBridging.h\"
+  #include \"swift/SILOptimizer/OptimizerBridging.h\"
+  ")
+  add_library(importedHeaderDependencies "${CMAKE_CURRENT_BINARY_DIR}/HeaderDependencies.cpp")
 
-# When building unified, we need to make sure all the Clang headers are
-# generated before we try to use them.
-# When building Swift against an already compiled LLVM/Clang, like
-# build-script does, this target does not exist, but the headers
-# are already completely generated at that point.
-if(TARGET clang-tablegen-targets)
-  add_dependencies(importedHeaderDependencies clang-tablegen-targets)
+  # When building unified, we need to make sure all the Clang headers are
+  # generated before we try to use them.
+  # When building Swift against an already compiled LLVM/Clang, like
+  # build-script does, this target does not exist, but the headers
+  # are already completely generated at that point.
+  if(TARGET clang-tablegen-targets)
+    add_dependencies(importedHeaderDependencies clang-tablegen-targets)
+  endif()
 endif()