Include climits to support musl libc

PATH_MAX constant is not visible from any of currently included header
files in system with musl libc, where compilation fails with an error
below. The constant is defined in limits.h which is directly include via
climits header file.

fdcache.cpp: In static member function 'static FILE* FdManager::MakeTempFile()':
fdcache.cpp:381:14: error: 'PATH_MAX' was not declared in this scope
  381 |     char cfn[PATH_MAX];
      |              ^~~~~~~~

Fixes: d67b83e671 ("Allow configuration for temporary files directory")

src/fdcache.cpp

@@ -21,6 +21,7 @@
 #include <cstdio>
 #include <cstdlib>
 #include <cerrno>
+#include <climits>
 #include <unistd.h>
 #include <sys/types.h>
 #include <dirent.h>