make: move extra builds to "build/extra/" subdirectories

misc/cross-compile-upx-with-podman/20-image-run-shell.sh

@@ -34,7 +34,9 @@ podman run "${flags[@]}" "$image" bash -l
 
 # now we can cross-compile UPX for Windows:
 #   cd /home/upx/src/upx
-#   rm -rf ./build/release-cross-mingw64
-#   make build/release-cross-mingw64
+#   rm -rf ./build/extra/cross-mingw64/release
+#   make build/extra/cross-mingw64/release
 
-# lots of other cross-compilers are installed; see "ls /usr/bin/*g++*"
+# lots of other cross-compilers are installed:
+#   - see "ls /usr/bin/*g++*"
+#   - see misc/cross-compile-upx-with-podman/build-all-inside-container.sh

misc/cross-compile-upx-with-podman/build-all-inside-container.sh

@@ -27,7 +27,7 @@ function run_config_and_build {
         # these old architectures do not support sanitize
         alpha-linux-gnu) cmake_config_flags=-DUPX_CONFIG_DISABLE_SANITIZE=ON ;;
         hppa-linux-gnu) cmake_config_flags=-DUPX_CONFIG_DISABLE_SANITIZE=ON ;;
-        # avoid link errors with Windows cross compilers; need to install some more support libs??
+        # avoid link errors with current MinGW-w64 versions
         i686-w64-mingw32) cmake_config_flags=-DUPX_CONFIG_DISABLE_SANITIZE=ON ;;
         x86_64-w64-mingw32) cmake_config_flags=-DUPX_CONFIG_DISABLE_SANITIZE=ON ;;
         # avoid warnings about arm libstdc++ ABI change in gcc-7

misc/rebuild-stubs-with-podman/20-image-run-shell.sh

@@ -47,11 +47,11 @@ podman run "${flags[@]}" "$image" bash -l
 
 # we can also build UPX in the container:
 #   cd /home/upx/src/upx
-#   rm -rf ./build/release
-#   make build/release
+#   rm -rf ./build/extra/gcc/release
+#   make build/extra/gcc/release
 #   # run tests
-#   ./build/release/upx --version
-#   make -C build/release test
+#   ./build/extra/gcc/release/upx --version
+#   make -C build/extra/gcc/release test
 
 # and we can also rebuild the UPX docs the container:
 #   cd /home/upx/src/upx