fix: openldap does not use Fedora build flags

- %configure introduces the correct flags, however we need* to set our
  custom CFLAGS before the actual run of ./configure, thus we request
  the flags explicitly using %set_build_flags
- dropping %{optflags} which is just a legacy version of
  %{build_cflags} which is already included in $set_build_flags set

* ./configure plays with the flags, hence customizing the CFLAGS after
  %configure does not have a desired effect

Resolves: #1548676

openldap.spec

@@ -12,7 +12,7 @@
 
 Name: openldap
 Version: 2.4.45
-Release: 12%{?dist}
+Release: 13%{?dist}
 Summary: LDAP support libraries
 License: OpenLDAP
 URL: http://www.openldap.org/
@@ -161,15 +161,9 @@ popd
 
 %build
 
-%ifarch s390 s390x
-  export CFLAGS="-fPIE"
-%else
-  export CFLAGS="-fpie"
-%endif
-export LDFLAGS="-pie"
-# avoid stray dependencies (linker flag --as-needed)
+%set_build_flags
 # enable experimental support for LDAP over UDP (LDAP_CONNECTIONLESS)
-export CFLAGS="${CFLAGS} %{optflags} -Wl,--as-needed,-z,relro,-z,now -DLDAP_CONNECTIONLESS"
+export CFLAGS="${CFLAGS} ${LDFLAGS} -Wl,--as-needed -DLDAP_CONNECTIONLESS"
 
 pushd openldap-%{version}
 %configure \
@@ -512,6 +506,10 @@ exit 0
 %{_mandir}/man3/*
 
 %changelog
+* Thu Mar  1 2018 Matus Honek <mhonek@redhat.com> - 2.4.45-13
+- fix: openldap does not use Fedora build flags
+  + makes use of redhat-rpm-config package
+
 * Wed Feb 28 2018 Matus Honek <mhonek@redhat.com> - 2.4.45-12
 - MozNSS Compat. Layer: fix: libldap tlsmc continues even after it fails to extract CA certificates (#1550110)