[build] Do not pass -sdk when building stdlib on Linux

Author: egorzhdan

stdlib/cmake/modules/SwiftSource.cmake

@@ -223,7 +223,7 @@ function(_add_target_variant_swift_compile_flags
     ${ARGN})
 
   # On Windows, we don't set SWIFT_SDK_WINDOWS_PATH_ARCH_{ARCH}_PATH, so don't include it.
-  if (NOT "${sdk}" STREQUAL "WINDOWS")
+  if (NOT "${sdk}" STREQUAL "WINDOWS" AND NOT "${sdk}" STREQUAL "LINUX")
     list(APPEND result "-sdk" "${SWIFT_SDK_${sdk}_ARCH_${arch}_PATH}")
   endif()