Fix build flags for dependencies (#14038)

PR https://github.com/redis/redis/pull/13916 introduced a regression -
by overriding the `CFLAGS` and `LDFLAGS` variables for all of the
dependencies hiredis and fast_float lost some of their compiler/linker
flags.

This PR makes it so we can pass additional CFLAGS/LDFLAGS to hiredis,
without overriding them as it contains a bit more complex Makefile. As
for fast_float - passing CFLAGS/LDFLAGS from outside now doesn't break
the expected behavior.

The build step in the CI was changed so that the MacOS is now build with
TLS to catch such errors in the future.

.github/workflows/ci.yml

@@ -54,7 +54,9 @@ jobs:
     steps:
     - uses: actions/checkout@v4
     - name: make
-      run: make REDIS_CFLAGS='-Werror'
+      # Fail build if there are warnings
+      # build with TLS just for compilation coverage
+      run: make REDIS_CFLAGS='-Werror' BUILD_TLS=yes
 
   build-32bit:
     runs-on: ubuntu-latest