Rename compiler configuration file to fix "nim check" within the repo

Prior to the change, "nim check" would fail on any file besides the
main nim.nim, because the include paths for the documentation were
not set correctly and this produced various compilation errors.

compiler/nim.cfg

@@ -0,0 +1,21 @@
+# Special configuration file for the Nim project
+
+hint[XDeclaredButNotUsed]:off
+path:"llvm"
+path:"$projectPath/.."
+
+path:"$lib/packages/docutils"
+
+define:booting
+import:testability
+
+@if windows:
+  cincludes: "$lib/wrappers/libffi/common"
+@end
+
+define:useStdoutAsStdmsg
+
+cs:partial
+#define:useNodeIds
+symbol:nimfix
+#gc:markAndSweep