qt: Fix build for newer versions (#13262)

For some reason, newer versions of qt fail to build because they cannot
find certain system libraries such as libatomic and libdl.

Leaving the qmake compiler set to gcc seems to fix the problem.

Fixes #13221

var/spack/repos/builtin/packages/qt/package.py

@@ -294,8 +294,6 @@ def patch(self):
     @when('@5')
     def patch(self):
         # Fix qmake compilers in the default mkspec
-        filter_file('^QMAKE_COMPILER .*', 'QMAKE_COMPILER = cc',
-                    'qtbase/mkspecs/common/g++-base.conf')
         filter_file('^QMAKE_CC .*', 'QMAKE_CC = cc',
                     'qtbase/mkspecs/common/g++-base.conf')
         filter_file('^QMAKE_CXX .*', 'QMAKE_CXX = c++',