MACOSXPPC: ScummVM 2.9.0 is now built with GCC 7.5.0 instead of 4.8.5

Still using one compiler that's part of the (easy to set up)
"Unofficial TenFourFox Development Toolkit" on OSX 10.4.

That same compiler is used for the external dependencies that we
bundle, except for SDL1.2 still being compiled with old base gcc-4.0,
for reasons documented in its build.sh script.

Author: dwatteau

config.sh

@@ -9,7 +9,7 @@ export PATH=/staticscummvm/bin:/usr/bin:/bin:/usr/sbin:/sbin
 export MACOSX_DEPLOYMENT_TARGET=10.4
 export SDKROOT=/Developer/SDKs/MacOSX10.4u.sdk
 
-CXX='/usr/local/bin/ccache /opt/macports-tff/bin/g++-mp-4.8' \
+CXX='/usr/local/bin/ccache /opt/macports-tff/bin/g++-mp-7' \
 AR=/opt/macports-tff/bin/ar \
 LD=/opt/macports-tff/bin/ld-97 \
 RANLIB=/opt/macports-tff/bin/ranlib \
@@ -45,7 +45,7 @@ LDFLAGS='-Wl,-macosx_version_min,10.4 -Wl,-headerpad_max_install_names -L/static
 
 # USE_CURL= because we don't trust this on old macOS
 /opt/macports-tff/bin/gmake USE_CURL=
-exit 0
+#exit 0
 
 /opt/macports-tff/bin/gmake USE_CURL= bundle