Fix sed -i compatibility in configure.ac

Apply the same macOS BSD sed fix from 7e867f6 to
configure.ac, so that users regenerating configure
from source also get the compatibility fix.

Author: zhangyue1818

configure.ac

@@ -3204,4 +3204,11 @@ AC_OUTPUT
 # The configure args contain '-Wl,-rpath,\$$ORIGIN`, when it falls
 # as a C literal string, it's invalid, so converting `\` to `\\`
 # to be correct for C program.
-sed -i '/define CONFIGURE_ARGS/s,\([[^\\]]\)\\\$\$,\1\\\\$$,g' src/include/pg_config.h
+case $build_os in
+darwin*)
+  sed -i '' '/define CONFIGURE_ARGS/s,\([[^\\]]\)\\\$\$,\1\\\\$$,g' src/include/pg_config.h
+  ;;
+*)
+  sed -i '/define CONFIGURE_ARGS/s,\([[^\\]]\)\\\$\$,\1\\\\$$,g' src/include/pg_config.h
+  ;;
+esac