Copy code from IMAKEINCLUDE to IMAKECPP to handle arguments
such as -E. Lets IMAKECPP=$(tc-getCPP) be usable.
--- a/imake.c
+++ b/imake.c
@@ -532,6 +532,12 @@
 			}
 	}
-	if ((p = getenv("IMAKECPP")))
+	if ((p = getenv("IMAKECPP"))) {
 		cpp = p;
+		for (; *p; p++)
+			if (*p == ' ') {
+				*p++ = '\0';
+				AddCppArg(p);
+			}
+	}
 	if ((p = getenv("IMAKEMAKE")))
 		make_argv[0] = p;