This is a Base make.conf for portage with grub & UEFI:


# These settings were set by the catalyst build script that automatically
# built this stage.
# Please consult /usr/share/portage/config/make.conf.example for a more
# detailed example.
COMMON_FLAGS="-O2 -pipe -march=native"
CFLAGS="${COMMON_FLAGS}"
CXXFLAGS="${COMMON_FLAGS}"
FCFLAGS="${COMMON_FLAGS}"
FFLAGS="${COMMON_FLAGS}"

# NOTE: This stage was built with the bindist USE flag enabled

# This sets the language of build output to English.
# Please keep this setting intact when reporting bugs.
LC_MESSAGES=C.utf8
MAKEOPTS="-j4"

GENTOO_MIRRORS="https://mirror.reenigne.net/gentoo/ \
    http://gentoo.mirrors.tera-byte.com/ \
    https://mirror.csclub.uwaterloo.ca/gentoo-distfiles/"

ACCEPT_LICENSE="@GPL-COMPATIBLE @FSF-APPROVED @OSI-APPROVED @MISC-FREE @FREE-SOFTWARE @FSF-APPROVED-OTHER @MISC-FREE-DOCS @FREE-DOCUMENTS @FREE @BINARY-REDISTRIBUTABLE @EULA"
USE="dist-kernel"


#-j$(nproc) is not recognized by portage
#march=x86-64-v3 can be used as another option over-march=native for modern x86 devices..