[gn build] Manually port ed07e1f

Author: aeubanks

llvm/utils/gn/secondary/llvm/include/llvm/Config/BUILD.gn

@@ -213,6 +213,7 @@ write_cmake_config("config") {
       "HAVE_SIGALTSTACK=",
       "HAVE_STRERROR_R=",
       "HAVE_SYSCONF=",
+      "HAVE_SYSEXITS_H=",
       "HAVE_SYS_IOCTL_H=",
       "HAVE_SYS_MMAN_H=",
       "HAVE_SYS_PARAM_H=",
@@ -249,6 +250,7 @@ write_cmake_config("config") {
       "HAVE_SIGALTSTACK=1",
       "HAVE_STRERROR_R=1",
       "HAVE_SYSCONF=1",
+      "HAVE_SYSEXITS_H=1",
       "HAVE_SYS_IOCTL_H=1",
       "HAVE_SYS_MMAN_H=1",
       "HAVE_SYS_PARAM_H=1",