Same with Percona XTraDB Cluster 5.5:

...
build-binary.sh:170:export CFLAGS="-fPIC -Wall -O3 -g -static-libgcc -fno-omit-frame-pointer -DPERCONA_INNODB_VERSION=$PERCONA_SERVER_VERSION $TARGET_CFLAGS ${ FLAGS:-}"
build-binary.sh:171:export CXXFLAGS="-O2 -fno-omit-frame-pointer -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fno-exceptions -DPERCONA_INNODB_VERSION=$PERCONA_SERVER_VERSION $TARGET_CFLAGS ${CXXFLAGS:-}"
build-dpkg.sh:102:export CFLAGS="-fPIC -Wall -O3 -g -static-libgcc -fno-omit-frame-pointer -DPERCONA_INNODB_VERSION=$PERCONA_SERVER_VERSION ${CFLAGS:-}"
build-dpkg.sh:103:export CXXFLAGS="-O2 -fno-omit-frame-pointer -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fno-exceptions -DPERCONA_INNODB_VERSION=$PERCONA_SERVER_VERSION ${CXXFLAGS:-}"
...

and 5.6:

openxs@ao756:~/bzr/pxc-5.6/build$ grep -rn FLAGS *
build-binary-nobzr.sh:17:TARGET_CFLAGS=''
build-binary-nobzr.sh:45:        TARGET_CFLAGS="-m32 -march=i686"
build-binary-nobzr.sh:155:export CFLAGS="-fPIC -Wall -O3 -g -static-libgcc -fno-omit-frame-pointer -DPERCONA_INNODB_VERSION=$PERCONA_SERVER_VERSION $TARGET_CFLAGS ${CFLAGS:-}"
build-binary-nobzr.sh:156:export CXXFLAGS="-O2 -fno-omit-frame-pointer -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -DPERCONA_INNODB_VERSION=$PERCONA_SERVER_VERSION $TARGET_CFLAGS ${CXXFLAGS:-}"
build-binary.sh:17:TARGET_CFLAGS=''
build-binary.sh:50:        TARGET_CFLAGS="-m32 -march=i686"
build-binary.sh:175:export CFLAGS="-fPIC -Wall -O3 -g -static-libgcc -fno-omit-frame-pointer -DPERCONA_INNODB_VERSION=$PERCONA_SERVER_VERSION $TARGET_CFLAGS ${ FLAGS:-}"
build-binary.sh:176:export CXXFLAGS="-O2 -fno-omit-frame-pointer -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -DPERCONA_INNODB_VERSION=$PERCONA_SERVER_VERSION $TARGET_CFLAGS ${CXXFLAGS:-}"
build-dpkg.sh:104:export CFLAGS="-fPIC -Wall -O3 -g -static-libgcc -fno-omit-frame-pointer -DPERCONA_INNODB_VERSION=$PERCONA_SERVER_VERSION ${CFLAGS:-}"
build-dpkg.sh:105:export CXXFLAGS="-O2 -fno-omit-frame-pointer -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -DPERCONA_INNODB_VERSION=$PERCONA_SERVER_VERSION ${CXXFLAGS:-}"
build-dpkg.sh:137:        DEB_CFLAGS_APPEND="$CFLAGS" DEB_CXXFLAGS_APPEND="$CXXFLAGS" \
build-rpm.sh:20:TARGET_CFLAGS=''
build-rpm.sh:40:        TARGET_CFLAGS="-m32 -march=i686"
build-rpm.sh:93:        TARGET_CFLAGS='-m32 -march=i686'
build-rpm.sh:130:export CFLAGS="-fPIC -Wall -O3 -g -static-libgcc -fno-omit-frame-pointer -DPERCONA_INNODB_VERSION=$PERCONA_SERVER_VERSION $TARGET_CFLAGS ${CFLAGS:-}"
build-rpm.sh:131:export CXXFLAGS="-O2 -fno-omit-frame-pointer -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -DPERCONA_INNODB_VERSION=$PERCONA_SERVER_VERSION $TARGET_CFLAGS ${CXXFLAGS:-}"
debian/rules:67:        CXX="$${UDF_CXX:-g++}" CXXFLAGS="$(CXXFLAGS) -I$(CURDIR)/release/include" \
percona-xtradb-cluster.spec:416:        CXXFLAGS="$CXXFLAGS -I$RPM_BUILD_DIR/%{src_dir}/release/include" \
percona-xtradb-cluster.spec:428:# name, finally a default.  RPM_OPT_FLAGS is assumed to be a part of the
percona-xtradb-cluster.spec:437:# This is a hack, $RPM_OPT_FLAGS on ia64 hosts contains flags which break
percona-xtradb-cluster.spec:441:RPM_OPT_FLAGS=
percona-xtradb-cluster.spec:447:export CFLAGS=${MYSQL_BUILD_CFLAGS:-${CFLAGS:-$RPM_OPT_FLAGS}}
percona-xtradb-cluster.spec:448:export CXXFLAGS=${MYSQL_BUILD_CXXFLAGS:-${CXXFLAGS:-$RPM_OPT_FLAGS -felide-constructors -fno-rtti}}
percona-xtradb-cluster.spec:449:export LDFLAGS=${MYSQL_BUILD_LDFLAGS:-${LDFLAGS:-}}
percona-xtradb-cluster.spec:468:  CFLAGS=`echo " ${CFLAGS} " | \
percona-xtradb-cluster.spec:474:  CXXFLAGS=`echo " ${CXXFLAGS} " | \
percona-xtradb-cluster.spec:553:  libgcc=`$CC $CFLAGS --print-libgcc-file`
percona-xtradb-cluster.spec:1406:- Modify CFLAGS and CXXFLAGS such that a debug build is not optimized.
percona-xtradb-cluster.spec:1467:- Add CFLAGS to gcc call with --print-libgcc-file, to make sure the
percona-xtradb-cluster.spec:1559:- Set $LDFLAGS from $MYSQL_BUILD_LDFLAGS
percona-xtradb-cluster.spec:1874:- CFLAGS and CXXFLAGS should honor RPM_OPT_FLAGS
rpm/mysql-dubious-exports.patch:101:         PROPERTIES LINK_FLAGS "${libmysql_link_flags}")

(other than debian/* part)