Qt4Macros: Added support for generated resource files

Using the QT4_ADD_RESOURCES() macro required the resource file to exist
already for dependency scanning.  This prevented the use of resource
files that are generated by cmake because it needs the file before
resolving the dependency.  This patch adds support for generated
resource files by not scanning the resource file for dependencies if it
doesn't exist yet.  The add_custom_command() to generate the resource
file should add the dependencies on the files used by the resource file.

Modules/Qt4Macros.cmake

@@ -182,11 +182,13 @@ MACRO (QT4_ADD_RESOURCES outfiles )
     GET_FILENAME_COMPONENT(infile ${it} ABSOLUTE)
     GET_FILENAME_COMPONENT(rc_path ${infile} PATH)
     SET(outfile ${CMAKE_CURRENT_BINARY_DIR}/qrc_${outfilename}.cxx)
+
+    SET(_RC_DEPENDS)
+    IF(EXISTS "${infile}")
       #  parse file for dependencies
       #  all files are absolute paths or relative to the location of the qrc file
       FILE(READ "${infile}" _RC_FILE_CONTENTS)
       STRING(REGEX MATCHALL "<file[^<]+" _RC_FILES "${_RC_FILE_CONTENTS}")
-    SET(_RC_DEPENDS)
       FOREACH(_RC_FILE ${_RC_FILES})
         STRING(REGEX REPLACE "^<file[^>]*>" "" _RC_FILE "${_RC_FILE}")
         IF(NOT IS_ABSOLUTE "${_RC_FILE}")
@@ -199,6 +201,12 @@ MACRO (QT4_ADD_RESOURCES outfiles )
       # again when dependencies need to be recomputed.
       QT4_MAKE_OUTPUT_FILE("${infile}" "" "qrc.depends" out_depends)
       CONFIGURE_FILE("${infile}" "${out_depends}" COPY_ONLY)
+    ELSE(EXISTS "${infile}")
+      # The .qrc file does not exist (yet). Let's add a dependency and hope
+      # that it will be generated later
+      SET(out_depends)
+    ENDIF(EXISTS "${infile}")
+
     ADD_CUSTOM_COMMAND(OUTPUT ${outfile}
       COMMAND ${QT_RCC_EXECUTABLE}
       ARGS ${rcc_options} -name ${outfilename} -o ${outfile} ${infile}