CMake LIBMTP Version Detection

[Alejandro Wainzinger]

Amarok needs libmtp version >= 0.3.0 to compile correctly, and in the
module this is tested for, and in the debug output during
configuration it appears to properly detect whether or not the version
requirement is met, but during compilation it seems to ignore this and
tries to build even if the version is < 0.3.0 .  I'm pasting the
FindMtp.cmake file here for convenience, but it's available at:
http://websvn.kde.org/trunk/extragear/multimedia/amarok/cmake/modules/FindMtp.cmake?revision=845877&view=markup

# - Try to find the libmtp library
# Once done this will define
#
#  MTP_FOUND - system has libmtp
#  MTP_INCLUDE_DIR - the libmtp include directory
#  MTP_LIBRARIES - Link these to use libmtp
#  MTP_DEFINITIONS - Compiler switches required for using libmtp
#

if (MTP_INCLUDE_DIR AND MTP_LIBRARIES AND MTP_VERSION_OKAY)

  # in cache already
  SET(MTP_FOUND TRUE)

else (MTP_INCLUDE_DIR AND MTP_LIBRARIES AND MTP_VERSION_OKAY)
  if(NOT WIN32)
    # use pkg-config to get the directories and then use these values
    # in the FIND_PATH() and FIND_LIBRARY() calls
    INCLUDE(UsePkgConfig)

    PKGCONFIG(libmtp _MTPIncDir _MTPLinkDir _MTPLinkFlags _MTPCflags)

    set(MTP_DEFINITIONS ${_MTPCflags})
  endif(NOT WIN32)
  FIND_PATH(MTP_INCLUDE_DIR libmtp.h
    ${_MTPIncDir}
  )

  FIND_LIBRARY(MTP_LIBRARIES NAMES mtp
    PATHS
    ${_MTPLinkDir}
  )

  exec_program(${PKGCONFIG_EXECUTABLE} ARGS --atleast-version=0.3.0
libmtp OUTPUT_VARIABLE _pkgconfigDevNull RETURN_VALUE
MTP_VERSION_OKAY)

  if (MTP_INCLUDE_DIR AND MTP_LIBRARIES AND MTP_VERSION_OKAY STREQUAL "0")
     set(MTP_FOUND TRUE)
  endif (MTP_INCLUDE_DIR AND MTP_LIBRARIES AND MTP_VERSION_OKAY STREQUAL "0")

  if (MTP_FOUND)
    if (NOT Mtp_FIND_QUIETLY)
      message(STATUS "Found MTP: ${MTP_LIBRARIES}")
    endif (NOT Mtp_FIND_QUIETLY)
  else (MTP_FOUND)
    if (MTP_INCLUDE_DIR AND MTP_LIBRARIES AND NOT MTP_VERSION_OKAY STREQUAL "0")
      message(STATUS "Found MTP but version requirements not met")
    endif (MTP_INCLUDE_DIR AND MTP_LIBRARIES AND NOT MTP_VERSION_OKAY
STREQUAL "0")
    if (Mtp_FIND_REQUIRED)
      message(FATAL_ERROR "Could NOT find MTP")
    endif (Mtp_FIND_REQUIRED)
  endif (MTP_FOUND)

  MARK_AS_ADVANCED(MTP_INCLUDE_DIR MTP_LIBRARIES MTP_VERSION_OKAY)

endif (MTP_INCLUDE_DIR AND MTP_LIBRARIES AND MTP_VERSION_OKAY)



And the following is checked in the appropriate CMakeLists.txt file:

macro_optional_find_package(Mtp)

# Old MTP stuff, which might be reverted to or reused to accompany old
libmtp cmake madness
#INCLUDE(FindPkgConfig)
#pkg_check_modules(Mtp libmtp>=0.3.0)

if (MTP_FOUND)
...


Any ideas?