Description of problem:

Building rstp doesn't honor $RPM_OPT_FLAGS/%optflags.

see https://bugzilla.redhat.com/attachment.cgi?id=1126054
and check all calls to gcc:
...
gcc -Wall -Werror -O2 -g -D_REENTRANT -D__LINUX__ -DVERSION=0.16 -DBUILD=1 -I. -I./include -I./rstplib   -c -o brstate.o brstate.c
...
gcc -g -O -Wall -D_REENTRANT -D__LINUX__   -c -o port.o port.c
...

Version-Release number of selected component (if applicable):
- rstp-04012009git-16.fc25
- Probably all versions of the rstp package in Fedora

How reproducible:
Always

Steps to Reproduce:
1. Build the package, check build.log


Additional info:
A brute-force patch would be this one:
# diff --git a/rstp.spec b/rstp.spec
index 9bcbc14..4d52a5c 100644
--- a/rstp.spec
+++ b/rstp.spec
@@ -35,6 +35,8 @@ replaces the in-kernel STP implementation
 %patch2 -p1
 %patch3 -p1
 
+sed -i -e 's|^\(CFLAGS = .*\)$|\1 %{optflags} |' Makefile */Makefile
+
 %build
 make %{?_smp_mflags}