build: Set PTHREAD_LIBS for pkgconfig files if empty
diff --git a/configure.ac b/configure.ac
index 770df2f..dc2720d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -509,6 +509,10 @@
 
 dnl Check for pthreads
 AX_PTHREAD
+dnl AX_PTHREADS leaves PTHREAD_LIBS empty for gcc and sets PTHREAD_CFLAGS
+dnl to -pthread, which causes problems if we need -lpthread to appear in
+dnl pkgconfig files.
+test -z "$PTHREAD_LIBS" && PTHREAD_LIBS="-lpthread"
 
 dnl SELinux awareness.
 AC_ARG_ENABLE([selinux],