Package building with gcc-10

[Hamzeh Nasajpour]

Hi guys.
I have a cpp Application that should be build with `gcc-toolchain-10.2.0`. I 
could build it in local. But seems that in package building the 
`cmake-build-system` is using the `gcc-7.5.0`. How can I set a specific version 
of gcc for building my package definition? 


```
...
/tmp/guix-build-my-cpp-app-0.1.1.drv-0/my-cpp-app/src/GUI/FileDownloader.h:27:10:
 fatal error: filesystem: No such file or directory
 #include <filesystem>
          ^~~~~~~~~~~~
compilation terminated.
make[2]: *** [CMakeFiles/my-cpp-app.dir/build.make:121: 
CMakeFiles/my-cpp-app.dir/src/GUI/ContentList.cpp.o] Error 1
make[2]: Leaving directory '/tmp/guix-build-my-cpp-app-0.1.1.drv-0/build'
make[1]: *** [CMakeFiles/Makefile2:208: CMakeFiles/my-cpp-app.dir/all] Error 2
make[1]: *** Waiting for unfinished jobs....
[ 69%] Linking CXX executable test_DataAccessLayer
/gnu/store/89rj5fqcg48afgk99639ds602pgf92k4-cmake-minimal-3.16.5/bin/cmake -E 
cmake_link_script CMakeFiles/test_DataAccessLayer.dir/link.txt --verbose=1
/gnu/store/rn75fm7adgx3pw5j8pg3bczfqq1y17lk-gcc-7.5.0/bin/c++   -Wall -O2 -g 
-DNDEBUG  -rdynamic 
CMakeFiles/test_DataAccessLayer.dir/test_DataAccessLayer_autogen/mocs_compilation.cpp.o
 CMakeFiles/test_DataAccessLayer.dir/tests/TestDataAccessLayer.cpp.o  -o 
test_DataAccessLayer  
/gnu/store/59dq1n4wj3maa3kcar6hspj2zd82as7q-qtbase-5.14.2/lib/libQt5Test.so.5.14.2
 lib_my-cpp-app.a 
/gnu/store/59dq1n4wj3maa3kcar6hspj2zd82as7q-qtbase-5.14.2/lib/libQt5Widgets.so.5.14.2
 
/gnu/store/59dq1n4wj3maa3kcar6hspj2zd82as7q-qtbase-5.14.2/lib/libQt5Gui.so.5.14.2
 
/gnu/store/59dq1n4wj3maa3kcar6hspj2zd82as7q-qtbase-5.14.2/lib/libQt5Network.so.5.14.2
 
/gnu/store/59dq1n4wj3maa3kcar6hspj2zd82as7q-qtbase-5.14.2/lib/libQt5Sql.so.5.14.2
 
/gnu/store/59dq1n4wj3maa3kcar6hspj2zd82as7q-qtbase-5.14.2/lib/libQt5DBus.so.5.14.2
 
/gnu/store/59dq1n4wj3maa3kcar6hspj2zd82as7q-qtbase-5.14.2/lib/libQt5Core.so.5.14.2
 -lrec 
[ 70%] Linking CXX executable test_AsyncTaskRunner
/gnu/store/89rj5fqcg48afgk99639ds602pgf92k4-cmake-minimal-3.16.5/bin/cmake -E 
cmake_link_script CMakeFiles/test_AsyncTaskRunner.dir/link.txt --verbose=1
/gnu/store/rn75fm7adgx3pw5j8pg3bczfqq1y17lk-gcc-7.5.0/bin/c++   -Wall -O2 -g 
-DNDEBUG  -rdynamic 
CMakeFiles/test_AsyncTaskRunner.dir/test_AsyncTaskRunner_autogen/mocs_compilation.cpp.o
 CMakeFiles/test_AsyncTaskRunner.dir/tests/TestAsyncTaskRunner.cpp.o  -o 
test_AsyncTaskRunner  
/gnu/store/59dq1n4wj3maa3kcar6hspj2zd82as7q-qtbase-5.14.2/lib/libQt5Test.so.5.14.2
 lib_my-cpp-app.a 
/gnu/store/59dq1n4wj3maa3kcar6hspj2zd82as7q-qtbase-5.14.2/lib/libQt5Widgets.so.5.14.2
 
/gnu/store/59dq1n4wj3maa3kcar6hspj2zd82as7q-qtbase-5.14.2/lib/libQt5Gui.so.5.14.2
 
/gnu/store/59dq1n4wj3maa3kcar6hspj2zd82as7q-qtbase-5.14.2/lib/libQt5Network.so.5.14.2
 
/gnu/store/59dq1n4wj3maa3kcar6hspj2zd82as7q-qtbase-5.14.2/lib/libQt5Sql.so.5.14.2
 
/gnu/store/59dq1n4wj3maa3kcar6hspj2zd82as7q-qtbase-5.14.2/lib/libQt5DBus.so.5.14.2
 
/gnu/store/59dq1n4wj3maa3kcar6hspj2zd82as7q-qtbase-5.14.2/lib/libQt5Core.so.5.14.2
 -lrec 
[ 72%] Linking CXX executable test_RecDB
/gnu/store/89rj5fqcg48afgk99639ds602pgf92k4-cmake-minimal-3.16.5/bin/cmake -E 
cmake_link_script CMakeFiles/test_RecDB.dir/link.txt --verbose=1
/gnu/store/rn75fm7adgx3pw5j8pg3bczfqq1y17lk-gcc-7.5.0/bin/c++   -Wall -O2 -g 
-DNDEBUG  -rdynamic 
CMakeFiles/test_RecDB.dir/test_RecDB_autogen/mocs_compilation.cpp.o 
CMakeFiles/test_RecDB.dir/tests/TestRecDB.cpp.o  -o test_RecDB  
/gnu/store/59dq1n4wj3maa3kcar6hspj2zd82as7q-qtbase-5.14.2/lib/libQt5Test.so.5.14.2
 lib_my-cpp-app.a 
/gnu/store/59dq1n4wj3maa3kcar6hspj2zd82as7q-qtbase-5.14.2/lib/libQt5Widgets.so.5.14.2
 
/gnu/store/59dq1n4wj3maa3kcar6hspj2zd82as7q-qtbase-5.14.2/lib/libQt5Gui.so.5.14.2
 
/gnu/store/59dq1n4wj3maa3kcar6hspj2zd82as7q-qtbase-5.14.2/lib/libQt5Network.so.5.14.2
 
/gnu/store/59dq1n4wj3maa3kcar6hspj2zd82as7q-qtbase-5.14.2/lib/libQt5Sql.so.5.14.2
 
/gnu/store/59dq1n4wj3maa3kcar6hspj2zd82as7q-qtbase-5.14.2/lib/libQt5DBus.so.5.14.2
 
/gnu/store/59dq1n4wj3maa3kcar6hspj2zd82as7q-qtbase-5.14.2/lib/libQt5Core.so.5.14.2
 -lrec 
make[2]: Leaving directory '/tmp/guix-build-my-cpp-app-0.1.1.drv-0/build'
[ 72%] Built target test_DataAccessLayer
make[2]: Leaving directory '/tmp/guix-build-my-cpp-app-0.1.1.drv-0/build'
[ 72%] Built target test_AsyncTaskRunner
make[2]: Leaving directory '/tmp/guix-build-my-cpp-app-0.1.1.drv-0/build'
[ 72%] Built target test_RecDB
[ 74%] Linking CXX executable test_PackageManager
/gnu/store/89rj5fqcg48afgk99639ds602pgf92k4-cmake-minimal-3.16.5/bin/cmake -E 
cmake_link_script CMakeFiles/test_PackageManager.dir/link.txt --verbose=1
/gnu/store/rn75fm7adgx3pw5j8pg3bczfqq1y17lk-gcc-7.5.0/bin/c++   -Wall -O2 -g 
-DNDEBUG  -rdynamic 
CMakeFiles/test_PackageManager.dir/test_PackageManager_autogen/mocs_compilation.cpp.o
 CMakeFiles/test_PackageManager.dir/tests/TestPackageManager.cpp.o  -o 
test_PackageManager  
/gnu/store/59dq1n4wj3maa3kcar6hspj2zd82as7q-qtbase-5.14.2/lib/libQt5Test.so.5.14.2
 lib_my-cpp-app.a 
/gnu/store/59dq1n4wj3maa3kcar6hspj2zd82as7q-qtbase-5.14.2/lib/libQt5Widgets.so.5.14.2
 
/gnu/store/59dq1n4wj3maa3kcar6hspj2zd82as7q-qtbase-5.14.2/lib/libQt5Gui.so.5.14.2
 
/gnu/store/59dq1n4wj3maa3kcar6hspj2zd82as7q-qtbase-5.14.2/lib/libQt5Network.so.5.14.2
 
/gnu/store/59dq1n4wj3maa3kcar6hspj2zd82as7q-qtbase-5.14.2/lib/libQt5Sql.so.5.14.2
 
/gnu/store/59dq1n4wj3maa3kcar6hspj2zd82as7q-qtbase-5.14.2/lib/libQt5DBus.so.5.14.2
 
/gnu/store/59dq1n4wj3maa3kcar6hspj2zd82as7q-qtbase-5.14.2/lib/libQt5Core.so.5.14.2
 -lrec 
make[2]: Leaving directory '/tmp/guix-build-my-cpp-app-0.1.1.drv-0/build'
[ 74%] Built target test_PackageManager
make[1]: Leaving directory '/tmp/guix-build-my-cpp-app-0.1.1.drv-0/build'

```