[cmake] Merge SwiftTranslateFlag.cmake into SwiftUtils.cmake

Both files are relatively small and contain utilities used by the build system.
So it makes sense to merge them.

Author: gottesmm

CMakeLists.txt

@@ -351,7 +351,7 @@ set(CMAKE_CXX_ARCHIVE_FINISH "")
 
 include(CheckCXXSourceRuns)
 include(CMakeParseArguments)
-include(SwiftTranslateFlag)
+include(SwiftUtils)
 include(SwiftHandleGybSources)
 include(SwiftSetIfArchBitness)
 include(SwiftSource)

cmake/modules/SwiftAddCustomCommandTarget.cmake

@@ -1,5 +1,5 @@
 include(CMakeParseArguments)
-include(SwiftTranslateFlag)
+include(SwiftUtils)
 
 # Populate the variable 'args' in the parent scope with a keyword
 # argument list.  We read the variables options, ${k}_keyword, and

cmake/modules/SwiftTranslateFlag.cmake

@@ -3,3 +3,31 @@ function(precondition var)
     message(FATAL_ERROR "Error! Variable ${var} is false or not set!")
   endif()
 endfunction()
+
+# Translate a yes/no variable to the presence of a given string in a
+# variable.
+#
+# Usage:
+#   translate_flag(is_set flag_name var_name)
+#
+# If is_set is true, sets ${var_name} to ${flag_name}. Otherwise,
+# unsets ${var_name}.
+function(translate_flag is_set flag_name var_name)
+  if(${is_set})
+    set("${var_name}" "${flag_name}" PARENT_SCOPE)
+  else()
+    set("${var_name}" "" PARENT_SCOPE)
+  endif()
+endfunction()
+
+macro(translate_flags prefix options)
+  foreach(var ${options})
+    translate_flag("${${prefix}_${var}}" "${var}" "${prefix}_${var}_keyword")
+  endforeach()
+endmacro()
+
+# Set ${outvar} to ${${invar}}, asserting if ${invar} is not set.
+function(precondition_translate_flag invar outvar)
+  precondition(${invar})
+  set(${outvar} "${${invar}}" PARENT_SCOPE)
+endfunction()