Fix most warnings that would be caused by gcc flag -Wundef

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5173 c046a42c-6fe2-441c-8c8c-71466251a162
diff --git a/elf.h b/elf.h
index 1bba022..861f1d3 100644
--- a/elf.h
+++ b/elf.h
@@ -1123,6 +1123,7 @@
   Elf64_Word n_type;	/* Content type */
 } Elf64_Nhdr;
 
+#ifdef ELF_CLASS
 #if ELF_CLASS == ELFCLASS32
 
 #define elfhdr		elf32_hdr
@@ -1165,5 +1166,7 @@
 # endif
 #endif
 
+#endif /* ELF_CLASS */
+
 
 #endif /* _QEMU_ELF_H */