build: append to the computed c_compile_flags

Adjust the `c_compile_flags` variable to ensure that the flags are ordered
correctly.  This is of import for the android build which may end up using
invalid header search path ordering otherwise.  This ensures that the path
for the ICU includes comes after the C++ headers which is necessary in new
C++ releases which shadow math.h

Author: compnerd

cmake/modules/AddSwift.cmake

@@ -1209,13 +1209,21 @@ function(_add_swift_library_single target name)
        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}_${SWIFTLIB_SINGLE_ARCHITECTURE}_ICU_UC_INCLUDE}")
+     if(SWIFT_COMPILER_IS_MSVC_LIKE)
+       list(APPEND c_compile_flags -I;${SWIFT_${SWIFTLIB_SINGLE_SDK}_${SWIFTLIB_SINGLE_ARCHITECTURE}_ICU_UC_INCLUDE})
+     else()
+       list(APPEND c_compile_flags -isystem;${SWIFT_${SWIFTLIB_SINGLE_SDK}_${SWIFTLIB_SINGLE_ARCHITECTURE}_ICU_UC_INCLUDE})
+     endif()
     endif()
     if(NOT "${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}_${SWIFTLIB_SINGLE_ARCHITECTURE}_ICU_I18N_INCLUDE}")
+     if(SWIFT_COMPILER_IS_MSVC_LIKE)
+       list(APPEND c_compile_flags -I;${SWIFT_${SWIFTLIB_SINGLE_SDK}_${SWIFTLIB_SINGLE_ARCHITECTURE}_ICU_I18N_INCLUDE})
+     else()
+       list(APPEND c_compile_flags -isystem;${SWIFT_${SWIFTLIB_SINGLE_SDK}_${SWIFTLIB_SINGLE_ARCHITECTURE}_ICU_I18N_INCLUDE})
+     endif()
     endif()
   endif()