The Nix glibc headers do not use include/x86_64-linux-gnu subdirectories. --- swift/stdlib/public/Platform/CMakeLists.txt 2019-04-09 20:14:44.493801403 +0200 +++ swift/stdlib/public/Platform/CMakeLists.txt 2019-04-09 20:14:44.577800593 +0200 @@ -68,7 +68,7 @@ endif() set(GLIBC_INCLUDE_PATH "${GLIBC_SYSROOT_RELATIVE_INCLUDE_PATH}") - set(GLIBC_ARCH_INCLUDE_PATH "${GLIBC_SYSROOT_RELATIVE_ARCH_INCLUDE_PATH}") + set(GLIBC_ARCH_INCLUDE_PATH "${GLIBC_SYSROOT_RELATIVE_INCLUDE_PATH}") if(NOT "${SWIFT_SDK_${sdk}_ARCH_${arch}_PATH}" STREQUAL "/" AND NOT "${sdk}" STREQUAL "ANDROID") set(GLIBC_INCLUDE_PATH "${SWIFT_SDK_${sdk}_ARCH_${arch}_PATH}${GLIBC_INCLUDE_PATH}")