Fix macro preprocessing for #include. Arguments enclosed in "" or <> must not

be preprocessed. See ISO/IEC 9899 1990 (E) section 6.8.2.

test/val/bug2458.c

@@ -0,0 +1,10 @@
+#define str(arg) #arg
+#include str(bug2458.h)         /* Ok, macro replacement */
+
+#define string foo
+#include <string.h>             /* Ok, no macro replacement */
+
+int main()
+{
+    return 0;
+}

test/val/bug2458.h

@@ -0,0 +1 @@
+