COMP: CMakeLists.txt - Fixes MAKE_CXX_COMPILER_ID compare statement

Either

IF(${CMAKE_CXX_COMPILER_ID} STREQUAL "GNU")

or

IF(DEFINED CMAKE_CXX_COMPILER_ID AND ${CMAKE_CXX_COMPILER_ID} STREQUAL "GNU")

should be used.

CMakeLists.txt

@@ -227,7 +227,7 @@ ENDIF()
 # Set coverage Flags
 #
 IF(WITH_COVERAGE)
-  IF(CMAKE_CXX_COMPILER_ID AND ${CMAKE_CXX_COMPILER_ID} STREQUAL "GNU")
+  IF(${CMAKE_CXX_COMPILER_ID} STREQUAL "GNU")
     SET(coverage_flags "-g -fdiagnostics-show-option -fprofile-arcs -ftest-coverage -O3 -DNDEBUG")
     SET(COVERAGE_CXX_FLAGS ${coverage_flags})
     SET(COVERAGE_C_FLAGS ${coverage_flags})
@@ -240,7 +240,7 @@ ENDIF()
 SET(CTK_C_FLAGS "${COVERAGE_C_FLAGS} ${ADDITIONAL_C_FLAGS}")
 SET(CTK_CXX_FLAGS "${VISIBILITY_CXX_FLAGS} ${COVERAGE_CXX_FLAGS} ${ADDITIONAL_CXX_FLAGS}")
 
-IF(CMAKE_CXX_COMPILER_ID AND ${CMAKE_CXX_COMPILER_ID} STREQUAL "GNU")
+IF(${CMAKE_CXX_COMPILER_ID} STREQUAL "GNU")
   SET(cflags "-fdiagnostics-show-option -Wall -Wextra -Wpointer-arith -Winvalid-pch -Wcast-align -Wwrite-strings -fstack-protector-all -D_FORTIFY_SOURCE=2")
   SET(CTK_C_FLAGS "${cflags} ${CTK_C_FLAGS}")
   SET(CTK_CXX_FLAGS "${cflags} -Woverloaded-virtual -Wold-style-cast -Wstrict-null-sentinel -Wsign-promo ${CTK_CXX_FLAGS}")