Allow building of just glxtrace library for ebuilds without GUI tools.

Updated from 4.0 version of patch to apply against 5.0.

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 17f3dce..3bba2a9 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -33,6 +33,7 @@ set (ENABLE_EGL true CACHE BOOL "Enable EGL support.")
 
 set (ENABLE_WAFFLE false CACHE BOOL "Enable WAFFLE support.")
 
+option (BUILD_LIB_ONLY "Build the glxtrace library only" OFF)
 
 ##############################################################################
 # Find dependencies
@@ -301,6 +302,8 @@ set (MD5_LIBRARIES md5_bundled)
 # - The packaged versions QJson are very old, and do not support NaN/Infinity.
 # - To make it easier to build the GUI on Windows and MacOSX, as there are no
 # binaries at all.
+if (NOT BUILD_LIB_ONLY)
+
 if (QT4_FOUND)
     add_definitions (-DQJSON_EXPORT=)
     add_subdirectory (thirdparty/qjson)
@@ -310,6 +313,8 @@ if (QT4_FOUND)
     set (QJSON_FOUND TRUE)
 endif ()
 
+endif (NOT BUILD_LIB_ONLY)
+
 # We use bundled headers for all Khronos APIs, to guarantee support for both
 # OpenGL and OpenGL ES at build time, because the OpenGL and OpenGL ES 1 APIs
 # are so intertwined that conditional compilation extremely difficult. This
diff --git a/retrace/CMakeLists.txt b/retrace/CMakeLists.txt
index 4e37979..2607ddf 100644
--- a/retrace/CMakeLists.txt
+++ b/retrace/CMakeLists.txt
@@ -11,6 +11,8 @@ include_directories (
 
 add_definitions (-DRETRACE)
 
+if (NOT BUILD_LIB_ONLY)
+
 add_custom_command (
     OUTPUT glretrace_gl.cpp
     COMMAND ${PYTHON_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/glretrace.py > ${CMAKE_CURRENT_BINARY_DIR}/glretrace_gl.cpp
@@ -282,3 +284,5 @@ if (WIN32)
 
     install (TARGETS d3dretrace RUNTIME DESTINATION bin)
 endif ()
+
+endif (NOT BUILD_LIB_ONLY)