$ cat /etc/portage/env/clang-no-polly
COMMON_FLAGS="-O3 -flto=thin -fno-plt -fno-semantic-interposition -frecord-gcc-switches -march=native -pipe"
CFLAGS="${COMMON_FLAGS}"
CXXFLAGS="${COMMON_FLAGS}"
FCFLAGS="${COMMON_FLAGS}"
FFLAGS="${COMMON_FLAGS}"

$ cat /etc/portage/env/clang-no-lto
COMMON_FLAGS="${COMMON_FLAGS} -fno-lto"

LTO_FLAGS="-fno-lto"
LTO_FLAGS_THIN="-fno-lto"

$ cat /etc/portage/env/O2
COMMON_FLAGS="${COMMON_FLAGS} -O2"

$ cat /etc/portage/env/lld
LDFLAGS="${LDFLAGS} -fuse-ld=lld"

$ cat /etc/portage/env/gcc
COMMON_FLAGS="-O2 -march=native"
CFLAGS="${COMMON_FLAGS}"
CXXFLAGS="${COMMON_FLAGS}"
LDFLAGS="-Wl,--as-needed"

CC="gcc"
CXX="g++"
CPP="gcc -E"
AR="ar"
NM="nm"
RANLIB="ranlib"