Include missing headers

[QuinaryDolphin]

Added <sys/stat.h> to fix the mismatched pointer types and implicitly declare stat() and S_ISBLK() to fix the errors below that I encountered while installing.

udevil.c:4783:21: error: passing argument 2 of ‘signal’ from incompatible pointer type [-Wincompatible-pointer-types]
udevil.c:4784:21: error: passing argument 2 of ‘signal’ from incompatible pointer type [-Wincompatible-pointer-types]
udevil.c:4923:22: error: passing argument 2 of ‘signal’ from incompatible pointer type [-Wincompatible-pointer-types]
udevil.c:4924:22: error: passing argument 2 of ‘signal’ from incompatible pointer type [-Wincompatible-pointer-types]
udevil.c:4925:22: error: passing argument 2 of ‘signal’ from incompatible pointer type [-Wincompatible-pointer-types]

error: implicit declaration of function ‘stat’; did you mean ‘strcat’? [-Wimplicit-function-declaration]
  943 |                                 stat( mount_source, &statbuf ) == 0 &&
      |                                 ^~~~
      |                                 strcat
device-info.c:944:33: error: implicit declaration of function ‘S_ISBLK’; did you mean ‘S_IFBLK’? [-Wimplicit-function-declaration]
  944 |                                 S_ISBLK( statbuf.st_mode ) )
      |                                 ^~~~~~~
      |                                 S_IFBLK