Description of problem:
Package gstreamermm fails to build from source in Fedora Rawhide.

Version-Release number of selected component (if applicable):
1.10.0-17.fc38

Steps to Reproduce:
koji build --scratch f38 gstreamermm-1.10.0-17.fc38.src.rpm

Additional info:
This package is tracked by Koschei. See:
https://koschei.fedoraproject.org/package/gstreamermm

Since 1.13.0, gtest requires C++14 or later. Possible solutions include:

- Patch gstreamermm to build with C++14 or later.
- Stop building the tests.
- Bundle a gtest 1.12.1 source archive and compile and link against that instead.

In file included from /usr/include/gtest/gtest-message.h:57,
                 from /usr/include/gtest/gtest-assertion-result.h:46,
                 from /usr/include/gtest/gtest.h:64,
                 from ../../tests/mmtest.h:4,
                 from ../../tests/test-bufferlist.cc:8:
/usr/include/gtest/internal/gtest-port.h:270:2: error: #error C++ versions less than C++14 are not supported.
  270 | #error C++ versions less than C++14 are not supported.
      |  ^~~~~