diff --git a/libc/cmake/modules/LLVMLibCArchitectures.cmake b/libc/cmake/modules/LLVMLibCArchitectures.cmake
index 6c730f807de6d..939fc1226a4e9 100644
--- a/libc/cmake/modules/LLVMLibCArchitectures.cmake
+++ b/libc/cmake/modules/LLVMLibCArchitectures.cmake
@@ -215,6 +215,37 @@ else()
           "Unsupported libc target operating system ${LIBC_TARGET_OS}")
 endif()
 
+# If the compiler target triple is not the same as the triple specified by
+# LIBC_TARGET_TRIPLE or LLVM_RUNTIMES_TARGET, we will add a --target option
+# if the compiler is clang. If the compiler is GCC we just error out as there
+# is no equivalent of an option like --target.
+if(explicit_target_triple AND
+   (NOT (libc_compiler_triple STREQUAL explicit_target_triple)))
+  set(LIBC_CROSSBUILD TRUE)
+  if(CMAKE_COMPILER_IS_GNUCXX)
+    message(FATAL_ERROR
+            "GCC target triple (${libc_compiler_triple}) and the explicity "
+            "specified target triple (${explicit_target_triple}) do not match.")
+  else()
+    list(APPEND
+         LIBC_COMPILE_OPTIONS_DEFAULT "--target=${explicit_target_triple}")
+  endif()
+endif()
+
+if(LIBC_TARGET_OS_IS_DARWIN)
+  execute_process(
+    COMMAND xcrun --sdk macosx --show-sdk-path
+    OUTPUT_VARIABLE MACOSX_SDK_PATH
+    RESULT_VARIABLE MACOSX_SDK_PATH_RESULT
+    OUTPUT_STRIP_TRAILING_WHITESPACE
+  )
+  if(MACOSX_SDK_PATH_RESULT EQUAL 0)
+    list(APPEND LIBC_COMPILE_OPTIONS_DEFAULT "-I" "${MACOSX_SDK_PATH}/usr/include")
+  else()
+    message(WARNING "Could not find macOS SDK path. `xcrun --sdk macosx --show-sdk-path` failed.")
+  endif()
+endif()
+
 # Windows does not support full mode build.
 if (LIBC_TARGET_OS_IS_WINDOWS AND LLVM_LIBC_FULL_BUILD)
   message(FATAL_ERROR "Windows does not support full mode build.")
diff --git a/libc/include/sys/syscall.h.def b/libc/include/sys/syscall.h.def
index 60e5024e500e3..f7e53cc4942d5 100644
--- a/libc/include/sys/syscall.h.def
+++ b/libc/include/sys/syscall.h.def
@@ -9,7 +9,7 @@
 #ifndef LLVM_LIBC_SYS_SYSCALL_H
 #define LLVM_LIBC_SYS_SYSCALL_H
 
-//TODO: Handle non-linux syscalls
+#if defined(__linux__)
 
 #include <asm/unistd.h>
 
@@ -2361,5 +2361,6 @@
 #define SYS_writev __NR_writev
 #endif
 
+#endif // __linux__
 
 #endif // LLVM_LIBC_SYS_SYSCALL_H
diff --git a/libc/test/UnitTest/ExecuteFunctionUnix.cpp b/libc/test/UnitTest/ExecuteFunctionUnix.cpp
index c0e85c2144005..7c2eb7c6e887c 100644
--- a/libc/test/UnitTest/ExecuteFunctionUnix.cpp
+++ b/libc/test/UnitTest/ExecuteFunctionUnix.cpp
@@ -57,9 +57,7 @@ ProcessStatus invoke_in_subprocess(FunctionCaller *func, int timeout_ms) {
   }
   ::close(pipe_fds[1]);
 
-  struct pollfd poll_fd {
-    pipe_fds[0], 0, 0
-  };
+  struct pollfd poll_fd{pipe_fds[0], POLLIN, 0};
   // No events requested so this call will only return after the timeout or if
   // the pipes peer was closed, signaling the process exited.
   if (::poll(&poll_fd, 1, timeout_ms) == -1) {