gdbm: --enable-libgdbm-compat

--enable-libgdbm-compat for dbm.h / gdbm-ndbm.h compatibility:
  https://www.gnu.org.ua/software/gdbm/manual/html_chapter/gdbm_19.html

Formula/gdbm.rb

@@ -5,6 +5,7 @@ class Gdbm < Formula
   mirror "https://ftpmirror.gnu.org/gdbm/gdbm-1.18.1.tar.gz"
   sha256 "86e613527e5dba544e73208f42b78b7c022d4fa5a6d5498bf18c8d6f745b91dc"
   license "GPL-3.0"
+  revision 1
 
   bottle do
     cellar :any
@@ -15,18 +16,25 @@ class Gdbm < Formula
     sha256 "89d6db4fbffbe2184b4531faaebf0432a4b01e1ed92678ce6bd2f95c69dc9803" => :sierra
   end
 
+  # --enable-libgdbm-compat for dbm.h / gdbm-ndbm.h compatibility:
+  #   https://www.gnu.org.ua/software/gdbm/manual/html_chapter/gdbm_19.html
   # Use --without-readline because readline detection is broken in 1.13
   # https://github.com/Homebrew/homebrew-core/pull/10903
   def install
     args = %W[
       --disable-dependency-tracking
       --disable-silent-rules
+      --enable-libgdbm-compat
       --without-readline
       --prefix=#{prefix}
     ]
 
     system "./configure", *args
     system "make", "install"
+
+    # Avoid conflicting with macOS SDK's ndbm.h.  Renaming to gdbm-ndbm.h
+    # matches Debian's convention for gdbm's ndbm.h (libgdbm-compat-dev).
+    mv include/"ndbm.h", include/"gdbm-ndbm.h"
   end
 
   test do