just zap all brew packages from the runner to avoid conflicts

.github/workflows/autobuild.yml

@@ -3,7 +3,7 @@ name: Automatic Build
 
 on:
   push:
-    branches: ['dev']
+    branches: ['autobuild']
 
 jobs:
   build-windows:
@@ -131,6 +131,9 @@ jobs:
         with:
           length: 7
 
+      - name: Remove pre-existing homebrew packages
+        run: brew remove --force $(brew list)
+
       - name: Checkout repository
         uses: actions/checkout@v3
 

macos/Dependencies/common.make

@@ -48,7 +48,6 @@ RUBY_CONFIGURE_ARGS := \
 	--with-out-ext=fiddle,gdbm,win32ole,win32 \
 	--with-static-linked-ext \
 	--disable-rubygems \
-	--without-gmp \
 	--disable-install-doc \
 	--build=$(RBUILD) \
 	${EXTRA_RUBY_CONFIG_ARGS}