Add 'extern' decl before variable test - some older compilers wont
mark a variable visible if an extern decl precedes it.
# Test if "visible" variables and functions are marked global.
cat - > $TMPFILE1 <<EOF
void __attribute__((externally_visible)) t1() { }
+extern unsigned char v1;
unsigned char v1 __attribute__((section(".data16.foo.19"))) __attribute__((externally_visible));
EOF
$CC -Os -c -fwhole-program $TMPFILE1 -o $TMPFILE1o > /dev/null 2>&1