add -fvisibility=hidden to CC flags, mark XXX_main functions

EXTERNALLY_VISIBLE. 5% size reduction of libbusybox.so

editors/awk.c

@@ -2752,7 +2752,7 @@ static rstream *next_input_file(void)
 #undef files_happen
 }
 
-int awk_main(int argc, char **argv);
+int awk_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int awk_main(int argc, char **argv)
 {
 	unsigned opt;

editors/cmp.c

@@ -42,7 +42,7 @@ static const char opt_chars[] ALIGN1 = "sl";
 #define CMP_OPT_s (1<<0)
 #define CMP_OPT_l (1<<1)
 
-int cmp_main(int argc, char **argv);
+int cmp_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int cmp_main(int argc, char **argv)
 {
 	FILE *fp1, *fp2, *outfile = stdout;

editors/diff.c

@@ -1207,7 +1207,7 @@ static void diffdir(char *p1, char *p2)
 #endif
 
 
-int diff_main(int argc, char **argv);
+int diff_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int diff_main(int argc, char **argv)
 {
 	bool gotstdin = 0;

editors/ed.c

@@ -88,7 +88,7 @@ static char *skip_blank(const char *cp)
 }
 
 
-int ed_main(int argc, char **argv);
+int ed_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int ed_main(int argc, char **argv)
 {
 	INIT_G();

editors/patch.c

@@ -77,7 +77,7 @@ static int file_doesnt_exist(const char *filename)
 	return stat(filename, &statbuf);
 }
 
-int patch_main(int argc, char **argv);
+int patch_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int patch_main(int argc, char **argv)
 {
 	int patch_level = -1;

editors/sed.c

@@ -1223,7 +1223,7 @@ static void add_cmd_block(char *cmdstr)
 	free(sv);
 }
 
-int sed_main(int argc, char **argv);
+int sed_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int sed_main(int argc, char **argv)
 {
 	enum {

editors/vi.c

@@ -311,7 +311,7 @@ static void write1(const char *out)
 	fputs(out, stdout);
 }
 
-int vi_main(int argc, char **argv);
+int vi_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int vi_main(int argc, char **argv)
 {
 	int c;