[OE-core] [thud 09/12] qemu: fix build issue on new hosts with glibc 2.30

This fixes the following error: TOPDIR/tmp/work/x86_64-linux/qemu-native/3.1.0-r0/qemu-3.1.0/linux-user/syscall.c:254:16: error: static declaration of ‘gettid’ follows non-static declaration 254 | _syscall0(int, gettid) |^~ TOPDIR/tmp/work/x86_64-linux/qemu-native/3.1.0-r0

[OE-core] [thud 09/12] qemu: fix build issue on new hosts with glibc 2.30

This fixes the following error: TOPDIR/tmp/work/x86_64-linux/qemu-native/3.1.0-r0/qemu-3.1.0/linux-user/syscall.c:254:16: error: static declaration of ‘gettid’ follows non-static declaration 254 | _syscall0(int, gettid) |^~ TOPDIR/tmp/work/x86_64-linux/qemu-native/3.1.0-r0