This is easy to confirm using grep:

openxs@ao756:~/bzr/percona-5.5/build-ps$ grep -n FLAGS *
build-binary.sh:17:TARGET_CFLAGS=''
build-binary.sh:48:        TARGET_CFLAGS="-m32 -march=i686"
build-binary.sh:157:export CFLAGS="-fPIC -Wall -O3 -g -static-libgcc -fno-omit-frame-pointer -DPERCONA_INNODB_VERSION=$PERCONA_SERVER_VERSION $TARGET_CFLAGS ${ FLAGS:-}"
build-binary.sh:158:export CXXFLAGS="-O2 -fno-omit-frame-pointer -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fno-exceptions -DPERCONA_INNODB_VERSION=$PERCONA_SERVER_VERSION $TARGET_CFLAGS ${CXXFLAGS:-}"
build-rpm.sh:20:TARGET_CFLAGS=''
build-rpm.sh:40:        TARGET_CFLAGS="-m32 -march=i686"
build-rpm.sh:93:        TARGET_CFLAGS='-m32 -march=i686'
build-rpm.sh:126:export CFLAGS="-fPIC -Wall -O3 -g -static-libgcc -fno-omit-frame-pointer -DPERCONA_INNODB_VERSION=$PERCONA_SERVER_VERSION $TARGET_CFLAGS ${CFLAGS:-}"
build-rpm.sh:127:export CXXFLAGS="-O2 -fno-omit-frame-pointer -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fno-exceptions -DPERCONA_INNODB_VERSION=$PERCONA_SERVER_VERSION $TARGET_CFLAGS ${CXXFLAGS:-}"
build-shared-compat-rpm.sh:21:TARGET_CFLAGS=''
build-shared-compat-rpm.sh:41:        TARGET_CFLAGS="-m32 -march=i686"
build-shared-compat-rpm.sh:89:        TARGET_CFLAGS='-m32 -march=i686'
build-shared-compat-rpm.sh:116:export CFLAGS="-fPIC -Wall -O3 -g -static-libgcc -fno-omit-frame-pointer $TARGET_CFLAGS"
build-shared-compat-rpm.sh:117:export CXXFLAGS="-O2 -fno-omit-frame-pointer -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fno-exceptions $TARGET_CFLAGS"
grep: debian: Is a directory
percona-server.spec:344:        MYSQL_CFLAGS="-I $RPM_BUILD_DIR/%{src_dir}/release/include" \
percona-server.spec:357:        CXXFLAGS="$CXXFLAGS -I$RPM_BUILD_DIR/%{src_dir}/release/include" \
percona-server.spec:369:# name, finally a default.  RPM_OPT_FLAGS is assumed to be a part of the
percona-server.spec:378:# This is a hack, $RPM_OPT_FLAGS on ia64 hosts contains flags which break
percona-server.spec:382:RPM_OPT_FLAGS=
percona-server.spec:388:export CFLAGS=${MYSQL_BUILD_CFLAGS:-${CFLAGS:-$RPM_OPT_FLAGS}}
percona-server.spec:389:export CXXFLAGS=${MYSQL_BUILD_CXXFLAGS:-${CXXFLAGS:-$RPM_OPT_FLAGS -felide-constructors -fno-exceptions -fno-rtti}}
percona-server.spec:390:export LDFLAGS=${MYSQL_BUILD_LDFLAGS:-${LDFLAGS:-}}
percona-server.spec:408:  CFLAGS=`echo " ${CFLAGS} " | \
percona-server.spec:414:  CXXFLAGS=`echo " ${CXXFLAGS} " | \
percona-server.spec:479:  libgcc=`$CC $CFLAGS --print-libgcc-file`
percona-server.spec:1341:- Modify CFLAGS and CXXFLAGS such that a debug build is not optimized.
percona-server.spec:1402:- Add CFLAGS to gcc call with --print-libgcc-file, to make sure the
percona-server.spec:1494:- Set $LDFLAGS from $MYSQL_BUILD_LDFLAGS
percona-server.spec:1809:- CFLAGS and CXXFLAGS should honor RPM_OPT_FLAGS
grep: rpm: Is a directory
openxs@ao756:~/bzr/percona-5.5/build-ps$ grep -n FLAGS debian/*
grep: debian/additions: Is a directory
grep: debian/patches: Is a directory
grep: debian/po: Is a directory
debian/rules:81:                CFLAGS=$${MYSQL_BUILD_CFLAGS:-"-O3 -DBIG_JOINS=1"} \
debian/rules:83:                CXXFLAGS=$${MYSQL_BUILD_CXXFLAGS:-"-O3 -DBIG_JOINS=1 -felide-constructors -fno-exceptions -fno-rtti"} \
grep: debian/source: Is a directory