mysql55: fix build under clang 6 (and newer)

pkgs/servers/sql/mysql/5.5.x.nix

@@ -1,5 +1,5 @@
-{ stdenv, fetchurl, cmake, bison, ncurses, openssl, readline, zlib, perl
-, cctools, CoreServices }:
+{ stdenv, fetchpatch, fetchurl, cmake, bison, ncurses, openssl
+, readline, zlib, perl, cctools, CoreServices }:
 
 # Note: zlib is not required; MySQL can use an internal zlib.
 
@@ -13,10 +13,17 @@ self = stdenv.mkDerivation rec {
     sha256 = "1mwrzwk9ap09s430fpdkyhvx5j2syd3xj2hyfzvanjphq4xqbrxi";
   };
 
-  patches = if stdenv.isCygwin then [
-    ./5.5.17-cygwin.patch
-    ./5.5.17-export-symbols.patch
-  ] else null;
+  patches =
+    # Minor type error that is a build failure as of clang 6.
+    stdenv.lib.optional stdenv.cc.isClang (fetchpatch {
+      url = "https://svn.freebsd.org/ports/head/databases/mysql55-server/files/patch-sql_sql_partition.cc?rev=469888";
+      extraPrefix = "";
+      sha256 = "09sya27z3ir3xy5mrv3x68hm274594y381n0i6r5s627x71jyszf";
+    }) ++
+    stdenv.lib.optionals stdenv.isCygwin [
+      ./5.5.17-cygwin.patch
+      ./5.5.17-export-symbols.patch
+    ];
 
   preConfigure = stdenv.lib.optional stdenv.isDarwin ''
     ln -s /bin/ps $TMPDIR/ps
@@ -51,7 +58,10 @@ self = stdenv.mkDerivation rec {
     "-DINSTALL_SQLBENCHDIR="
   ];
 
-  NIX_CFLAGS_COMPILE = [ "-fpermissive" ]; # since gcc-7
+  NIX_CFLAGS_COMPILE =
+    stdenv.lib.optionals stdenv.cc.isGNU [ "-fpermissive" ] # since gcc-7
+    ++ stdenv.lib.optionals stdenv.cc.isClang [ "-Wno-c++11-narrowing" ]; # since clang 6
+
   NIX_LDFLAGS = stdenv.lib.optionalString stdenv.isLinux "-lgcc_s";
 
   prePatch = ''
@@ -78,6 +88,6 @@ self = stdenv.mkDerivation rec {
       artistic1 bsd0 bsd2 bsd3 bsdOriginal
       gpl2 lgpl2 lgpl21 mit publicDomain  licenses.zlib
     ];
-    broken = stdenv.isAarch64 && stdenv.isDarwin;
+    broken = stdenv.isAarch64;
   };
 }; in self