--- libcxx-11.0.0.mainline.ebuild	2020-11-30 15:51:51.000000000 -0600
+++ libcxx-11.0.0.ebuild	2020-12-09 19:02:46.000000000 -0600
@@ -14,9 +14,10 @@
 
 LICENSE="Apache-2.0-with-LLVM-exceptions || ( UoI-NCSA MIT )"
 SLOT="0"
-KEYWORDS="amd64 arm arm64 x86"
-IUSE="elibc_glibc elibc_musl +libcxxabi +libunwind +static-libs test"
-REQUIRED_USE="libunwind? ( libcxxabi )"
+KEYWORDS="amd64 arm arm64 x86 ~x64-macos"
+IUSE="elibc_Darwin elibc_glibc elibc_musl +libcxxabi +libunwind +static-libs test bootstrap"
+REQUIRED_USE="libunwind? ( libcxxabi )
+	elibc_Darwin? ( libcxxabi )"
 RESTRICT="!test? ( test )"
 
 RDEPEND="
@@ -41,7 +42,7 @@
 }
 
 pkg_setup() {
-	llvm_pkg_setup
+	use bootstrap || llvm_pkg_setup
 	use test && python-any-r1_pkg_setup
 
 	if ! use libcxxabi && ! tc-is-gcc ; then
@@ -58,6 +59,11 @@
 	eapply "${FILESDIR}/${PN}-3.9-cmake-link-flags.patch"
 
 	llvm.org_src_prepare
+
+	# eprefixify static path references to libc++abi for symbol re-export to
+	# avoid linking against it twice in both /usr/lib and ${EPREFIX}/usr/lib
+	local lcpa=/usr/lib/libc++abi.dylib
+	sed -i -e "s,${lcpa},${EPREFIX}${lcpa},g" lib/CMakeLists.txt
 }
 
 test_compiler() {
@@ -100,6 +106,8 @@
 			fi
 		fi
 	fi
+	# Darwin has libunwind in its system
+	[[ ${CHOST} == *-darwin* ]] && want_gcc_s=OFF
 
 	# bootstrap: cmake is unhappy if compiler can't link to stdlib
 	local nolib_flags=( -nodefaultlibs -lc )
@@ -188,8 +196,10 @@
 
 multilib_src_install() {
 	cmake_src_install
-	gen_shared_ldscript
-	use static-libs && gen_static_ldscript
+	if [[ ${CHOST} != *-darwin* ]] ; then
+		gen_shared_ldscript
+		use static-libs && gen_static_ldscript
+	fi
 }
 
 pkg_postinst() {