[CMake] Disable Regex literal when Swift parser integration is disabled

Regex literal parsing is now built as a part of ASTGen, that requires
host toolchain and swift-syntax integration.

(cherry picked from commit ee982fd)

Author: rintaro

CMakeLists.txt

@@ -270,10 +270,6 @@ option(SWIFT_BUILD_PERF_TESTSUITE
     "Create in-tree targets for building swift performance benchmarks."
     FALSE)
 
-option(SWIFT_BUILD_REGEX_PARSER_IN_COMPILER
-    "Build the Swift regex parser as part of the compiler."
-    TRUE)
-
 option(SWIFT_INCLUDE_TESTS "Create targets for building/running tests." TRUE)
 
 option(SWIFT_INCLUDE_TEST_BINARIES
@@ -696,6 +692,14 @@ option(SWIFT_BUILD_SWIFT_SYNTAX
   "Enable building swift syntax"
   FALSE)
 
+option(SWIFT_BUILD_REGEX_PARSER_IN_COMPILER
+    "Build the Swift regex parser as part of the compiler."
+    TRUE)
+if(SWIFT_BUILD_REGEX_PARSER_IN_COMPILER AND NOT SWIFT_BUILD_SWIFT_SYNTAX)
+  message(WARNING "Force setting SWIFT_BUILD_REGEX_PARSER_IN_COMPILER=OFF because Swift parser integration is disabled")
+  set(SWIFT_BUILD_REGEX_PARSER_IN_COMPILER OFF)
+endif()
+
 set(SWIFT_BUILD_HOST_DISPATCH FALSE)
 if(SWIFT_ENABLE_DISPATCH AND NOT CMAKE_SYSTEM_NAME STREQUAL "Darwin")
   # Only build libdispatch for the host if the host tools are being built and