boot-qemu.py: Check gdb_bin earlier

Otherwise, the call to sys.exit() in die() does not work and we end up
hanging.

Additionally, move it out of the while loop, as it does not make send to
check for gdb_bin every single time we want to invoke it.

Reported-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>

Author: nathanchance

boot-qemu.py

@@ -754,6 +754,8 @@ def launch_qemu(cfg):
     pretty_print_qemu_info(qemu_cmd[0])
 
     if gdb:
+        utils.check_cmd(gdb_bin)
+
         while True:
             utils.check_cmd("lsof")
             lsof = subprocess.run(["lsof", "-i:1234"],
@@ -766,7 +768,6 @@ def launch_qemu(cfg):
             utils.green("Starting QEMU with GDB connection on port 1234...")
             with subprocess.Popen(qemu_cmd + ["-s", "-S"]) as qemu_process:
                 utils.green("Starting GDB...")
-                utils.check_cmd(gdb_bin)
                 gdb_cmd = [gdb_bin]
                 gdb_cmd += [kernel_location.joinpath("vmlinux")]
                 gdb_cmd += ["-ex", "target remote :1234"]