CMake Gcov c++ creating wrong .gcno files

I have a CMakeLists.txt file in which I added:

set(CMAKE_CXX_FLAGS "-fprofile-arcs -ftest-coverage -pthread -std=c++11 -O0 ${CMAKE_CXX_FLAGS}")

It is generating the report files in:

project_root/build/CMakeFiles/project.dir/

BUT the files it generates have extentions .cpp.gcno, .cpp.gcda and .cpp.o.

Also, they are not in the same folder as the src files, which are at:

project_root/src/ 

When I move the report files to the src/ folder and execute

$ gcov main.cpp
main.gcno:cannot open notes file

But I get that error message. So I change the .cpp.gcno, .cpp.cdna and cpp.o to .gcno, .gcda and .o and finally I get the following:

gcov main.cpp
Lines executed:86.67% of 15
Creating 'main.cpp.gcov'

I have over 50 files and can't do this manually for each one.

I need to be able to run gcov once for all files and generate report for all files. I don't care where the files are generated.