[485131] Fix incorrect detection of FreeBSD and OpenBSD

Thanks to Peter Morjan.

Bug: https://bugs.eclipse.org/bugs/show_bug.cgi?id=485131

ChangeLog.txt

@@ -6,6 +6,7 @@ Broker:
   use. Closes #487178.
 - Fix detection of broken connections on Windows. Closes #485143.
 - Close stdin etc. when daemonised. Closes #485589.
+- Fix incorrect detection of FreeBSD and OpenBSD. Closes #485131.
 
 Client library:
 - mosq->want_write should be cleared immediately before a call to SSL_write,

config.mk

@@ -115,7 +115,7 @@ LIB_LDFLAGS:=${LDFLAGS}
 BROKER_CFLAGS:=${LIB_CFLAGS} ${CPPFLAGS} -DVERSION="\"${VERSION}\"" -DTIMESTAMP="\"${TIMESTAMP}\"" -DWITH_BROKER
 CLIENT_CFLAGS:=${CFLAGS} ${CPPFLAGS} -I../lib -DVERSION="\"${VERSION}\""
 
-ifneq ($(or $(find $(UNAME),FreeBSD), $(find $(UNAME),OpenBSD)),)
+ifneq ($(or $(findstring $(UNAME),FreeBSD), $(findstring $(UNAME),OpenBSD)),)
 	BROKER_LIBS:=-lm
 else
 	BROKER_LIBS:=-ldl -lm