[test-suite, CUDA] Fix some CMake problems

[Hahnfeld]

Summary

1. The regex was matching any number in the path which is a problem if your path to external/ had numbers in it. I think this was because of the wrong string escape.
2. If /thrust does not exist, the variable isn't set at all. Avoid failure on EXIST with empty path by using DEFINED.

External/CUDA/CMakeLists.txt

set(SUPPORTED_GPU_CUDA_9_2
   sm_70 sm_72)
 
 # Helper macro to extract version number at the end of the string
 # Input: get_version(Var String)
 #    Where String = /some/string/with/version-x.y.z
 # Output:
 #    Sets Var=x.y.z
 macro(get_version Var Path)
-    string(REGEX MATCH "[0-9]+(\.[0-9]+)+" ${Var} ${Path})
+    string(REGEX MATCH "[0-9]+(\\.[0-9]+)+" ${Var} ${Path})
 endmacro (get_version)
 
 # Helper function to glob CUDA source files and set LANGUAGE property
 # to CXX on each of them. Sets Var in parent scope to the list of
 # files found.
 macro(cuda_glob Var)
   file(GLOB FileList ${ARGN})
   foreach(File IN LISTS FileList)
function(create_cuda_test_variant Std VariantSuffix)
   list(APPEND LDFLAGS ${_Cuda_LDFLAGS} ${_Std_LDFLAGS} ${_Stdlib_LDFLAGS})
 
   # Create a separate test target for simple tests that can be built/tested quickly.
   add_custom_target(cuda-tests-simple-${VariantSuffix}
     COMMENT "Build Simple CUDA tests for ${VariantSuffix}")
   create_local_cuda_tests(${VariantSuffix})
   add_dependencies(cuda-tests-simple cuda-tests-simple-${VariantSuffix})
 
-  if(EXISTS ${THRUST_PATH} AND (NOT ${Std} STREQUAL "c++14"))
+  if(DEFINED THRUST_PATH AND (NOT ${Std} STREQUAL "c++14"))
     create_thrust_tests(${VariantSuffix})
   endif()
 
   # Target for CUDA tests that take little time to build and run.
   add_custom_target(check-cuda-simple-${VariantSuffix}
     COMMAND ${TEST_SUITE_LIT} ${TEST_SUITE_LIT_FLAGS}
             ${CUDA_SIMPLE_TEST_TARGETS}
     WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}