package: GCC 9 and lcov from git work again.

And GCC 6 doesn't, so kill it. However the thing is even slower than
before, how the heck is that possible.

package/archlinux/PKGBUILD-coverage

@@ -7,7 +7,7 @@ arch=('i686' 'x86_64')
 url="https://magnum.graphics"
 license=('MIT')
 depends=('corrade' 'magnum' 'python')
-makedepends=('cmake' 'ninja' 'pybind11' 'lcov' 'gcc6')
+makedepends=('cmake' 'ninja' 'pybind11' 'lcov')
 provides=('magnum-bindings-git')
 
 _rootdir=$startdir/../../
@@ -21,7 +21,6 @@ build() {
     export CXXFLAGS="$newcxxflags"
 
     cmake .. \
-        -DCMAKE_CXX_COMPILER=g++-6 \
         -DCMAKE_CXX_FLAGS="--coverage" \
         -DCMAKE_BUILD_TYPE=Debug \
         -DCMAKE_INSTALL_PREFIX=/usr \
@@ -50,8 +49,8 @@ check() {
     rm -rf coverage
     mkdir coverage
     # Keep in sync with package/ci/travis-desktop.sh, please
-    lcov --gcov-tool="gcov-6" --directory . --capture --output-file coverage.info
-    lcov --gcov-tool="gcov-6" --extract coverage.info "*/src/python/*" --output-file coverage.info
+    lcov --directory . --capture --output-file coverage.info
+    lcov --extract coverage.info "*/src/python/*" --output-file coverage.info
     genhtml --output-directory ./coverage coverage.info
 }