Fix some warnings that would be generated by gcc -Wmissing-prototypes

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5022 c046a42c-6fe2-441c-8c8c-71466251a162
diff --git a/exec.c b/exec.c
index 3ab4ad0..a0aa7dc 100644
--- a/exec.c
+++ b/exec.c
@@ -386,7 +386,7 @@
 static uint8_t static_code_gen_buffer[DEFAULT_CODE_GEN_BUFFER_SIZE];
 #endif
 
-void code_gen_alloc(unsigned long tb_size)
+static void code_gen_alloc(unsigned long tb_size)
 {
 #ifdef USE_STATIC_CODE_GEN_BUFFER
     code_gen_buffer = static_code_gen_buffer;