[syscall] Build properly for the host, not just Fuchsia

Cobalt recently took a dependency on glog for a host tool. This broke
the OS X build, since the config.h file was made to run only for
Fuchsia.

Change-Id: I395e9da8fe420f6fb66b6ee42d75461b68c8d0fb
diff --git a/src/config.h b/src/config.h
index c513b41..721660e 100644
--- a/src/config.h
+++ b/src/config.h
@@ -83,7 +83,11 @@
 #define HAVE_STRING_H 1
 
 /* Define to 1 if you have the <syscall.h> header file. */
+#if defined(__Fuchsia__) || defined(__APPLE__)
 /* undef HAVE_SYSCALL_H */
+#else
+#define HAVE_SYSCALL_H 1
+#endif
 
 /* Define to 1 if you have the <syslog.h> header file. */
 #define HAVE_SYSLOG_H 1
@@ -92,7 +96,11 @@
 #define HAVE_SYS_STAT_H 1
 
 /* Define to 1 if you have the <sys/syscall.h> header file. */
-/* #undef HAVE_SYS_SYSCALL_H */
+#if defined(__Fuchsia__)
+/* undef HAVE_SYS_SYSCALL_H */
+#else
+#define HAVE_SYS_SYSCALL_H 1
+#endif
 
 /* Define to 1 if you have the <sys/time.h> header file. */
 #define HAVE_SYS_TIME_H 1
@@ -107,7 +115,11 @@
 #define HAVE_SYS_UTSNAME_H 1
 
 /* Define to 1 if you have the <ucontext.h> header file. */
+#if defined(__APPLE__)
+/* #undef HAVE_SYS_UCONTEXT_H */
+#else
 #define HAVE_UCONTEXT_H 1
+#endif
 
 /* Define to 1 if you have the <unistd.h> header file. */
 #define HAVE_UNISTD_H 1