[ci skip] Only set coverage option if COVERAGE==1

CMakeLists.txt

@@ -191,7 +191,7 @@ else()
 SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -fPIC")
 endif()
 
-if (UNIX)
+if (UNIX AND $ENV{COVERAGE} EQUALS 1)
       message("Setting coverage compiler options")
       SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -g -O0") # debug, no optimisation
       SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} --coverage") # enabling coverage