properly set build flags in rawhide (bz1543819)

libvpx.spec

@@ -6,7 +6,7 @@
 Name:			libvpx
 Summary:		VP8/VP9 Video Codec SDK
 Version:		1.7.0
-Release:		4%{?dist}
+Release:		5%{?dist}
 License:		BSD
 Group:			System Environment/Libraries
 #Source0:		http://downloads.webmproject.org/releases/webm/%{name}-%{version}.tar.bz2
@@ -80,6 +80,11 @@ and decoder.
 %global	generic_target 0
 %endif
 
+# only found in Fedora 28+
+%if 0%{?fedora} >= 28
+%set_build_flags
+%endif
+
 %ifarch armv7hl
 CROSS=armv7hl-redhat-linux-gnueabi- CHOST=armv7hl-redhat-linux-gnueabi-hardfloat ./configure \
 %else
@@ -231,6 +236,9 @@ rm -rf %{buildroot}%{_prefix}/src
 %{_bindir}/*
 
 %changelog
+* Mon Feb 12 2018 Tom Callaway <spot@fedoraproject.org> - 1.7.0-5
+- properly set build flags in rawhide (bz1543819)
+
 * Wed Feb 07 2018 Fedora Release Engineering <releng@fedoraproject.org> - 1.7.0-4
 - Rebuilt for https://fedoraproject.org/wiki/Fedora_28_Mass_Rebuild