bgp-perf needs libm for fmax(3) on various arch (seems to use an LLVM

intrinsic on amd64 aarch64 and maybe RISC-V); add unconditionally
ok tb@

net/bgp-perf/Makefile

@@ -1,6 +1,7 @@
 COMMENT =		OpenBGPD performance test suite
 
 VERSION =		0.0pl20251230
+REVISION =		0
 DISTNAME =		bgp-perf-${VERSION}
 
 GH_ACCOUNT =		openbgpd-portable
@@ -12,11 +13,15 @@ CATEGORIES =		net
 # ISC
 PERMIT_PACKAGE =	Yes
 
-WANTLIB +=		c util
+WANTLIB +=		c m util
 
 MAKE_FLAGS =		BINDIR="${TRUEPREFIX}/bin" \
 			MANDIR="${TRUEPREFIX}/man/man"
 
+# -lm needed for fmax on at least i386, sparc64;
+# uses llvm.maxnum intrinsic on amd64/aarch64 and maybe RISC-V
+MAKE_FLAGS =		LDFLAGS="-lm"
+
 NO_TEST =		Yes
 
 .include <bsd.port.mk>