CI: Set the verbose option in the Makefile to print compiling commands. (#1187)

Enable the verbose option in the Makefile used to compile the extension to
print the compiling command lines in the log.

Note that we use MAKEFLAGS rather than GNUMAKEFLAGS[1], because the
GNUMAKEFLAGS doesn't work for the make used in CI MacOS cases.

We don't need to set the verbose option to the CI Fedora and CentOS cases
(`.github/workflows/container.yml`). Because the Rubies from the Ruby RPM
package used in Fedora and CentOS cases are already enabling the verbose option.

[1] https://www.gnu.org/software/make/manual/html_node/Options_002fRecursion.html

Author: junaruga

.github/workflows/build.yml

@@ -63,6 +63,8 @@ jobs:
         run: echo "127.0.0.1 mysql2gem.example.com" | tee -a C:/Windows/System32/drivers/etc/hosts
       - run: echo 'DB=${{ matrix.db }}' >> $GITHUB_ENV
       - run: bash ci/setup.sh
+      # Set the verbose option in the Makefile to print compiling command lines.
+      - run: echo "MAKEFLAGS=V=1" >> $GITHUB_ENV
       - if: matrix.ssl
         run: echo "rake_spec_opts=--with-openssl-dir=$(brew --prefix ${{ matrix.ssl }})" >> $GITHUB_ENV
       - run: bundle exec rake spec -- $rake_spec_opts