[benchmark][cmake] Move runcmd from AddSwiftBench* => SwiftBenchmarkUtils.cmake.

A quick NFC cleanup that I saw.

rdar://40541972

benchmark/cmake/modules/AddSwiftBenchmarkSuite.cmake

@@ -2,24 +2,6 @@
 include(CMakeParseArguments)
 include(SwiftBenchmarkUtils)
 
-# Run a shell command and assign output to a variable or fail with an error.
-# Example usage:
-#   runcmd(COMMAND "xcode-select" "-p"
-#          VARIABLE xcodepath
-#          ERROR "Unable to find current Xcode path")
-function(runcmd)
-  cmake_parse_arguments(RUNCMD "" "VARIABLE;ERROR" "COMMAND" ${ARGN})
-  execute_process(
-      COMMAND ${RUNCMD_COMMAND}
-      OUTPUT_VARIABLE ${RUNCMD_VARIABLE}
-      RESULT_VARIABLE result
-      ERROR_QUIET OUTPUT_STRIP_TRAILING_WHITESPACE)
-  if(NOT "${result}" MATCHES "0")
-    message(FATAL_ERROR "${RUNCMD_ERROR}")
-  endif()
-  set(${RUNCMD_VARIABLE} ${${RUNCMD_VARIABLE}} PARENT_SCOPE)
-endfunction(runcmd)
-
 function (add_swift_benchmark_library objfile_out sibfile_out)
   cmake_parse_arguments(BENCHLIB "" "MODULE_PATH;SOURCE_DIR;OBJECT_DIR" "SOURCES;LIBRARY_FLAGS;DEPENDS" ${ARGN})
 

benchmark/cmake/modules/SwiftBenchmarkUtils.cmake

@@ -43,3 +43,22 @@ function(translate_flag is_set flag_name var_name)
     set("${var_name}" "" PARENT_SCOPE)
   endif()
 endfunction()
+
+
+# Run a shell command and assign output to a variable or fail with an error.
+# Example usage:
+#   runcmd(COMMAND "xcode-select" "-p"
+#          VARIABLE xcodepath
+#          ERROR "Unable to find current Xcode path")
+function(runcmd)
+  cmake_parse_arguments(RUNCMD "" "VARIABLE;ERROR" "COMMAND" ${ARGN})
+  execute_process(
+      COMMAND ${RUNCMD_COMMAND}
+      OUTPUT_VARIABLE ${RUNCMD_VARIABLE}
+      RESULT_VARIABLE result
+      ERROR_QUIET OUTPUT_STRIP_TRAILING_WHITESPACE)
+  if(NOT "${result}" MATCHES "0")
+    message(FATAL_ERROR "${RUNCMD_ERROR}")
+  endif()
+  set(${RUNCMD_VARIABLE} ${${RUNCMD_VARIABLE}} PARENT_SCOPE)
+endfunction(runcmd)