Refine header check in bin/varnishd/mgt/mgt.h, mgt_main.c for uClibc

Because of the difference in how uClibc and glibc stack their header
files, stdio.h indirectly brings in PTHREAD_CANCELED from pthread.h
on a uClibc system, whereas it does not on a glibc system.  This happens
in mgt.h and mgt_main.c.  This patch refines the check in those files
to take this fact into consideration.

X-Gentoo-Bug-URL: https://bugs.gentoo.org/444294
---

diff --git a/bin/varnishd/mgt.h b/bin/varnishd/mgt.h
index 905fbcc..5d3ab09 100644
--- a/bin/varnishd/mgt.h
+++ b/bin/varnishd/mgt.h
@@ -126,6 +126,6 @@ extern unsigned mgt_vcc_unsafe_path;
 		syslog(pri, fmt, __VA_ARGS__);		\
 	} while (0)
 
-#if defined(PTHREAD_CANCELED) || defined(PTHREAD_MUTEX_DEFAULT)
+#if (defined(PTHREAD_CANCELED) && !defined(__UCLIBC__)) || defined(PTHREAD_MUTEX_DEFAULT)
 #error "Keep pthreads out of in manager process"
 #endif
diff --git a/bin/varnishd/varnishd.c b/bin/varnishd/varnishd.c
index 1b7f1e3..dce42d9 100644
--- a/bin/varnishd/varnishd.c
+++ b/bin/varnishd/varnishd.c
@@ -656,6 +656,6 @@ main(int argc, char * const *argv)
 	exit(exit_status);
 }
 
-#if defined(PTHREAD_CANCELED) || defined(PTHREAD_MUTEX_DEFAULT)
+#if (defined(PTHREAD_CANCELED) && !defined(__UCLIBC__)) || defined(PTHREAD_MUTEX_DEFAULT)
 #error "Keep pthreads out of in manager process"
 #endif