Only include necessary file for include libs

The previous behavior caused a "Too many files open" error when
referrencing lots of libs because of the call to "gorge". This
modification retains the old behavior and also works if the library is
compiled locally.

nimgen.nim

@@ -501,13 +501,14 @@ proc c2nim(fl, outfile: string, c2nimConfig: c2nimConfigObj) =
     outpragma = ""
 
   passC = "import strutils\n"
-  for inc in gIncludes:
-    passC &= ("""{.passC: "-I\"" & gorge("nimble path $#").strip() & "/$#\"".}""" % [gOutput, inc]) & "\n"
+  passC &= "import ospaths\n"
 
   for prag in c2nimConfig.pragma:
     outpragma &= "{." & prag & ".}\n"
 
   let fname = file.splitFile().name.replace(re"[\.\-]", "_")
+  let fincl = file.replace(gOutput, "")
+
   if c2nimConfig.dynlib.len() != 0:
     let
       win = "when defined(Windows):\n"
@@ -537,7 +538,10 @@ proc c2nim(fl, outfile: string, c2nimConfig: c2nimConfigObj) =
     if outlib != "":
       extflags &= " --dynlib:dynlib$#" % fname
   else:
-    passC &= "const header$# = \"$#\"\n" % [fname, fl]
+    if file.isAbsolute():
+      passC &= "const header$# = \"$#\"\n" % [fname, fincl]
+    else:
+      passC &= "const header$# = currentSourcePath().splitPath().head & \"/$#\"\n" % [fname, fincl]
     extflags = "--header:header$#" % fname
 
   # Run c2nim on generated file