toolchain: instrument external toolchain wrapper

If BR_DEBUG_WRAPPER is set in the envirnment, dump the actual command
being exec()uted, to ease debugging issues with the wrapper.

[Peter: adjust code style and output format to be cut'n'paste compatible]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

toolchain/toolchain-external/ext-toolchain-wrapper.c

@@ -136,6 +136,15 @@ int main(int argc, char **argv)
 	/* finish with NULL termination */
 	*cur = NULL;
 
+	if (getenv("BR_DEBUG_WRAPPER")) {
+		fprintf(stderr, "Executing");
+
+		for (i = 0; args[i]; i++)
+			fprintf(stderr, " %s", args[i]);
+
+		fprintf(stderr, "\n");
+	}
+
 	if (execv(path, args))
 		perror(path);