Add MAKE_INSTALL_OPTS for packages

Allows for passing environment variables specifically to the "make install"
step of package building.

This can be helpful for providing a different DESTDIR= to a ruby install from
the --prefix that is used

bin/ruby-build

@@ -398,6 +398,8 @@ build_package_standard() {
   local PACKAGE_CONFIGURE_OPTS_ARRAY="${package_var_name}_CONFIGURE_OPTS_ARRAY[@]"
   local PACKAGE_MAKE_OPTS="${package_var_name}_MAKE_OPTS"
   local PACKAGE_MAKE_OPTS_ARRAY="${package_var_name}_MAKE_OPTS_ARRAY[@]"
+  local PACKAGE_MAKE_INSTALL_OPTS="${package_var_name}_MAKE_INSTALL_OPTS"
+  local PACKAGE_MAKE_INSTALL_OPTS_ARRAY="${package_var_name}_MAKE_INSTALL_OPTS_ARRAY[@]"
   local PACKAGE_CFLAGS="${package_var_name}_CFLAGS"
 
   [ "$package_var_name" = "RUBY" ] && use_homebrew_readline || true
@@ -409,7 +411,7 @@ build_package_standard() {
   ) >&4 2>&1
 
   { "$MAKE" $MAKE_OPTS ${!PACKAGE_MAKE_OPTS} "${!PACKAGE_MAKE_OPTS_ARRAY}"
-    "$MAKE" install
+    "$MAKE" install ${!PACKAGE_MAKE_INSTALL_OPTS} "${!PACKAGE_MAKE_INSTALL_OPTS_ARRAY}"
   } >&4 2>&1
 }