cmake: Replace invalid UTF-8 byte sequence

- Change the encoding of the regex temp placeholder token to UTF-8.

Prior to this change the file contained special chars in a different
encoding than ASCII or UTF-8 making text editors and Python complain
when reading the file.

Closes https://github.com/curl/curl/pull/1271
Closes https://github.com/curl/curl/pull/1275

CMakeLists.txt

@@ -1043,9 +1043,9 @@ function(TRANSFORM_MAKEFILE_INC INPUT_FILE OUTPUT_FILE)
   string(REPLACE "$(top_srcdir)"   "\${CURL_SOURCE_DIR}" MAKEFILE_INC_TEXT ${MAKEFILE_INC_TEXT})
   string(REPLACE "$(top_builddir)" "\${CURL_BINARY_DIR}" MAKEFILE_INC_TEXT ${MAKEFILE_INC_TEXT})
 
-  string(REGEX REPLACE "\\\\\n" "§!§" MAKEFILE_INC_TEXT ${MAKEFILE_INC_TEXT})
+  string(REGEX REPLACE "\\\\\n" "!π!α!" MAKEFILE_INC_TEXT ${MAKEFILE_INC_TEXT})
   string(REGEX REPLACE "([a-zA-Z_][a-zA-Z0-9_]*)[\t ]*=[\t ]*([^\n]*)" "SET(\\1 \\2)" MAKEFILE_INC_TEXT ${MAKEFILE_INC_TEXT})
-  string(REPLACE "§!§" "\n" MAKEFILE_INC_TEXT ${MAKEFILE_INC_TEXT})
+  string(REPLACE "!π!α!" "\n" MAKEFILE_INC_TEXT ${MAKEFILE_INC_TEXT})
 
   string(REGEX REPLACE "\\$\\(([a-zA-Z_][a-zA-Z0-9_]*)\\)" "\${\\1}" MAKEFILE_INC_TEXT ${MAKEFILE_INC_TEXT})    # Replace $() with ${}
   string(REGEX REPLACE "@([a-zA-Z_][a-zA-Z0-9_]*)@" "\${\\1}" MAKEFILE_INC_TEXT ${MAKEFILE_INC_TEXT})    # Replace @@ with ${}, even if that may not be read by CMake scripts.