build: sink the ICU flag handling lower (NFC)

Move the ICU flag handling to the same area as `_c_compile_variant_flags` which
computes the C compile flags.  This allows us to ensure that we order the flags
correctly when they are merged into the `c_compile_flags`.

Author: compnerd

cmake/modules/AddSwift.cmake

@@ -960,21 +960,6 @@ function(_add_swift_library_single target name)
   endif()
   _set_target_prefix_and_suffix("${target}" "${libkind}" "${SWIFTLIB_SINGLE_SDK}")
 
-  if(SWIFTLIB_SINGLE_TARGET_LIBRARY)
-    if(NOT "${SWIFT_${SWIFTLIB_SINGLE_SDK}_${SWIFTLIB_SINGLE_ARCHITECTURE}_ICU_UC_INCLUDE}" STREQUAL "" AND
-       NOT "${SWIFT_${SWIFTLIB_SINGLE_SDK}_${SWIFTLIB_SINGLE_ARCHITECTURE}_ICU_UC_INCLUDE}" STREQUAL "/usr/include" AND
-       NOT "${SWIFT_${SWIFTLIB_SINGLE_SDK}_${SWIFTLIB_SINGLE_ARCHITECTURE}_ICU_UC_INCLUDE}" STREQUAL "/usr/${SWIFT_SDK_${SWIFTLIB_SINGLE_SDK}_ARCH_${SWIFTLIB_SINGLE_ARCHITECTURE}_TRIPLE}/include" AND
-       NOT "${SWIFT_${SWIFTLIB_SINGLE_SDK}_${SWIFTLIB_SINGLE_ARCHITECTURE}_ICU_UC_INCLUDE}" STREQUAL "/usr/${SWIFT_SDK_${SWIFT_HOST_VARIANT_SDK}_ARCH_${SWIFT_HOST_VARIANT_ARCH}_TRIPLE}/include")
-     target_include_directories("${target}" SYSTEM PRIVATE "${SWIFT_${SWIFTLIB_SINGLE_SDK}_${SWIFTLIB_SINGLE_ARCHITECTURE}_ICU_UC_INCLUDE}")
-    endif()
-    if(NOT "${SWIFT_${SWIFTLIB_SINGLE_SDK}_${SWIFTLIB_SINGLE_ARCHITECTURE}_ICU_I18N_INCLUDE}" STREQUAL "" AND
-       NOT "${SWIFT_${SWIFTLIB_SINGLE_SDK}_${SWIFTLIB_SINGLE_ARCHITECTURE}_ICU_I18N_INCLUDE}" STREQUAL "/usr/include" AND
-       NOT "${SWIFT_${SWIFTLIB_SINGLE_SDK}_${SWIFTLIB_SINGLE_ARCHITECTURE}_ICU_I18N_INCLUDE}" STREQUAL "/usr/${SWIFT_SDK_${SWIFTLIB_SINGLE_SDK}_ARCH_${SWIFTLIB_SINGLE_ARCHITECTURE}_TRIPLE}/include" AND
-       NOT "${SWIFT_${SWIFTLIB_SINGLE_SDK}_${SWIFTLIB_SINGLE_ARCHITECTURE}_ICU_I18N_INCLUDE}" STREQUAL "/usr/${SWIFT_SDK_${SWIFT_HOST_VARIANT_SDK}_ARCH_${SWIFT_HOST_VARIANT_ARCH}_TRIPLE}/include")
-     target_include_directories("${target}" SYSTEM PRIVATE "${SWIFT_${SWIFTLIB_SINGLE_SDK}_${SWIFTLIB_SINGLE_ARCHITECTURE}_ICU_I18N_INCLUDE}")
-    endif()
-  endif()
-
   if("${SWIFTLIB_SINGLE_SDK}" STREQUAL "WINDOWS")
     swift_windows_include_for_arch(${SWIFTLIB_SINGLE_ARCHITECTURE} SWIFTLIB_INCLUDE)
     target_include_directories("${target}" SYSTEM PRIVATE ${SWIFTLIB_INCLUDE})
@@ -1219,6 +1204,21 @@ function(_add_swift_library_single target name)
     RESULT_VAR_NAME c_compile_flags
     )
 
+  if(SWIFTLIB_SINGLE_TARGET_LIBRARY)
+    if(NOT "${SWIFT_${SWIFTLIB_SINGLE_SDK}_${SWIFTLIB_SINGLE_ARCHITECTURE}_ICU_UC_INCLUDE}" STREQUAL "" AND
+       NOT "${SWIFT_${SWIFTLIB_SINGLE_SDK}_${SWIFTLIB_SINGLE_ARCHITECTURE}_ICU_UC_INCLUDE}" STREQUAL "/usr/include" AND
+       NOT "${SWIFT_${SWIFTLIB_SINGLE_SDK}_${SWIFTLIB_SINGLE_ARCHITECTURE}_ICU_UC_INCLUDE}" STREQUAL "/usr/${SWIFT_SDK_${SWIFTLIB_SINGLE_SDK}_ARCH_${SWIFTLIB_SINGLE_ARCHITECTURE}_TRIPLE}/include" AND
+       NOT "${SWIFT_${SWIFTLIB_SINGLE_SDK}_${SWIFTLIB_SINGLE_ARCHITECTURE}_ICU_UC_INCLUDE}" STREQUAL "/usr/${SWIFT_SDK_${SWIFT_HOST_VARIANT_SDK}_ARCH_${SWIFT_HOST_VARIANT_ARCH}_TRIPLE}/include")
+     target_include_directories("${target}" SYSTEM PRIVATE "${SWIFT_${SWIFTLIB_SINGLE_SDK}_${SWIFTLIB_SINGLE_ARCHITECTURE}_ICU_UC_INCLUDE}")
+    endif()
+    if(NOT "${SWIFT_${SWIFTLIB_SINGLE_SDK}_${SWIFTLIB_SINGLE_ARCHITECTURE}_ICU_I18N_INCLUDE}" STREQUAL "" AND
+       NOT "${SWIFT_${SWIFTLIB_SINGLE_SDK}_${SWIFTLIB_SINGLE_ARCHITECTURE}_ICU_I18N_INCLUDE}" STREQUAL "/usr/include" AND
+       NOT "${SWIFT_${SWIFTLIB_SINGLE_SDK}_${SWIFTLIB_SINGLE_ARCHITECTURE}_ICU_I18N_INCLUDE}" STREQUAL "/usr/${SWIFT_SDK_${SWIFTLIB_SINGLE_SDK}_ARCH_${SWIFTLIB_SINGLE_ARCHITECTURE}_TRIPLE}/include" AND
+       NOT "${SWIFT_${SWIFTLIB_SINGLE_SDK}_${SWIFTLIB_SINGLE_ARCHITECTURE}_ICU_I18N_INCLUDE}" STREQUAL "/usr/${SWIFT_SDK_${SWIFT_HOST_VARIANT_SDK}_ARCH_${SWIFT_HOST_VARIANT_ARCH}_TRIPLE}/include")
+     target_include_directories("${target}" SYSTEM PRIVATE "${SWIFT_${SWIFTLIB_SINGLE_SDK}_${SWIFTLIB_SINGLE_ARCHITECTURE}_ICU_I18N_INCLUDE}")
+    endif()
+  endif()
+
   if(SWIFTLIB_IS_STDLIB)
     # We don't ever want to link against the ABI-breakage checking symbols
     # in the standard library, runtime, or overlays because they only rely