Initialize c compiler variables later ...

... so that symbols such as "cpp" are defined

Fixes #1460

compiler/cgen.nim

@@ -486,7 +486,7 @@ proc lenField(p: BProc): PRope =
 include ccgcalls, "ccgstmts.nim", "ccgexprs.nim"
 
 # ----------------------------- dynamic library handling -----------------
-# We don't finalize dynamic libs as this does the OS for us.
+# We don't finalize dynamic libs as the OS does this for us.
 
 proc isGetProcAddr(lib: PLib): bool =
   let n = lib.path

compiler/main.nim

@@ -54,6 +54,7 @@ proc commandDoc2 =
   finishDoc2Pass(gProjectName)
 
 proc commandCompileToC =
+  extccomp.initVars()
   semanticPasses()
   registerPass(cgenPass)
   rodPass()