pseudotalloc: Add simplistic implementation of talloc_asprintf

fsm.c uses this function. When compiled with --enable-embedded, it
triggers a warning:

fsm.c: In function 'osmo_fsm_inst_alloc':
fsm.c:213:4: warning: implicit declaration of function 'talloc_asprintf' [-Wimplicit-function-declaration]
    fi->name = talloc_asprintf(fi, "%s(%s)", fsm->name, id);

Change-Id: I61cd83d4c8570af1e452c945ac6f194baf7e6ac4

src/pseudotalloc/pseudotalloc.c

@@ -5,6 +5,7 @@
 
 #include "talloc.h"
 #include <string.h>
+#include <stdio.h>
 
 void *_talloc_zero(const void *ctx, size_t size, const char *name)
 {
@@ -61,3 +62,18 @@ void *_talloc_zero_array(const void *ctx, size_t el_size, unsigned count, const
 {
 	return talloc_zero_size(ctx, el_size * count);
 }
+
+char *talloc_asprintf(const void *ctx, const char *fmt, ...)
+{
+	char *buf;
+	size_t len = 128;
+	va_list args;
+	va_start(args, fmt);
+
+	buf = talloc_size(ctx, len);
+	if (len < vsnprintf(buf, len, fmt, args))
+		strcpy(&buf[len-6], "[...]");
+
+	va_end(args);
+	return buf;
+}

src/pseudotalloc/talloc.h

@@ -39,4 +39,4 @@ void *_talloc_zero_array(const void *ctx,
 			 size_t el_size,
 			 unsigned count,
 			 const char *name);
-
+char *talloc_asprintf(const void *ctx, const char *fmt, ...);