Compile error on glibc-2.38-23

[pbsds]

/usr/include/string.h:380:14: error: conflicting types for 'strcasestr'; have 'char *(const char *, const char *)'
  380 | extern char *strcasestr (const char *__haystack, const char *__needle)
      |              ^~~~~~~~~~
mimetex.c:428:13: note: previous declaration of 'strcasestr' with type 'const char *(const char *, const char *)'
  428 | const char *strcasestr(const char *s1, const char *s2);

Removing the const from const char *strcasestr seems to fix it.