Do not use xenv from LCG

toolchain.cmake

@@ -18,4 +18,12 @@ if(NOT CMAKE_SOURCE_DIR MATCHES "CMakeTmp")
     message(FATAL_ERROR "Cannot find GaudiToolchainMacros.cmake")
   endif()
 
+  # FIXME: make sure we do not pick up unwanted/problematic projects from LCG
+  if(CMAKE_PREFIX_PATH)
+    # - ninja (it requires LD_LIBRARY_PATH set to run)
+    # - Gaudi (we do not want to use it from LCG)
+    # - xenv (conflicts with the version in the build environment)
+    list(FILTER CMAKE_PREFIX_PATH EXCLUDE REGEX "(LCG_|lcg/nightlies).*(ninja|Gaudi|xenv)")
+  endif()
+
 endif()