Unify the detection of Unix-like platforms

We were using slightly different guards to decide whether to include
`<unistd.h>` in different places. Unify those.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

ChangeLog.d/unistd.txt

@@ -0,0 +1,3 @@
+Changes
+   * Tweak the detection of Unix-like platforms, which makes more system
+     interfaces (timing, threading) available on Haiku, QNX and Midipix.

library/common.h

@@ -27,6 +27,21 @@
 #define MBEDTLS_HAVE_NEON_INTRINSICS
 #endif
 
+/* Decide whether we're built for a Unix-like platform.
+ */
+#if defined(_WIN32)
+/* If Windows platform interfaces are available, we use them, even if
+ * a Unix-like might also to be available. */
+/* defined(_WIN32) ==> we can include <windows.h> */
+#elif defined(unix) || defined(__unix) || defined(__unix__) ||    \
+    (defined(__APPLE__) && defined(__MACH__)) ||                  \
+    defined(__HAIKU__) ||                                         \
+    defined(__midipix__) ||                                       \
+    /* Add other Unix-like platform indicators here ^^^^ */ 0
+/* defined(MBEDTLS_PLATFORM_IS_UNIXLIKE) ==> we can include <unistd.h> */
+#define MBEDTLS_PLATFORM_IS_UNIXLIKE
+#endif
+
 /** Helper to define a function as static except when building invasive tests.
  *
  * If a function is only used inside its own source file and should be

library/net_sockets.c

@@ -19,9 +19,7 @@
 
 #if defined(MBEDTLS_NET_C)
 
-#if !defined(unix) && !defined(__unix__) && !defined(__unix) && \
-    !defined(__APPLE__) && !defined(_WIN32) && !defined(__QNXNTO__) && \
-    !defined(__HAIKU__) && !defined(__midipix__)
+#if !defined(MBEDTLS_PLATFORM_IS_UNIXLIKE) && !defined(_WIN32)
 #error "This module only works on Unix and Windows, see MBEDTLS_NET_C in mbedtls_config.h"
 #endif
 

library/platform_util.c

@@ -147,12 +147,9 @@ void mbedtls_zeroize_and_free(void *buf, size_t len)
 
 #if defined(MBEDTLS_HAVE_TIME_DATE) && !defined(MBEDTLS_PLATFORM_GMTIME_R_ALT)
 #include <time.h>
-#if !defined(_WIN32) && (defined(unix) || \
-    defined(__unix) || defined(__unix__) || (defined(__APPLE__) && \
-    defined(__MACH__)) || defined(__midipix__))
+#if defined(MBEDTLS_PLATFORM_IS_UNIXLIKE)
 #include <unistd.h>
-#endif /* !_WIN32 && (unix || __unix || __unix__ ||
-        * (__APPLE__ && __MACH__) || __midipix__) */
+#endif
 
 #if !((defined(_POSIX_VERSION) && _POSIX_VERSION >= 200809L) ||     \
     (defined(_POSIX_THREAD_SAFE_FUNCTIONS) &&                     \
@@ -218,12 +215,10 @@ void (*mbedtls_test_hook_test_fail)(const char *, int, const char *);
 #if defined(MBEDTLS_HAVE_TIME) && !defined(MBEDTLS_PLATFORM_MS_TIME_ALT)
 
 #include <time.h>
-#if !defined(_WIN32) && \
-    (defined(unix) || defined(__unix) || defined(__unix__) || \
-    (defined(__APPLE__) && defined(__MACH__)) || defined(__HAIKU__) || defined(__midipix__))
+#if defined(MBEDTLS_PLATFORM_IS_UNIXLIKE)
 #include <unistd.h>
-#endif \
-    /* !_WIN32 && (unix || __unix || __unix__ || (__APPLE__ && __MACH__) || __HAIKU__ || __midipix__) */
+#endif
+
 #if (defined(_POSIX_VERSION) && _POSIX_VERSION >= 199309L) || defined(__HAIKU__)
 mbedtls_ms_time_t mbedtls_ms_time(void)
 {

library/threading.c

@@ -21,9 +21,7 @@
 
 #if defined(MBEDTLS_HAVE_TIME_DATE) && !defined(MBEDTLS_PLATFORM_GMTIME_R_ALT)
 
-#if !defined(_WIN32) && (defined(unix) || \
-    defined(__unix) || defined(__unix__) || (defined(__APPLE__) && \
-    defined(__MACH__)))
+#if defined(MBEDTLS_PLATFORM_IS_UNIXLIKE)
 #include <unistd.h>
 #endif /* !_WIN32 && (unix || __unix || __unix__ ||
         * (__APPLE__ && __MACH__)) */

library/timing.c

@@ -13,9 +13,7 @@
 
 #if !defined(MBEDTLS_TIMING_ALT)
 
-#if !defined(unix) && !defined(__unix__) && !defined(__unix) && \
-    !defined(__APPLE__) && !defined(_WIN32) && !defined(__QNXNTO__) && \
-    !defined(__HAIKU__) && !defined(__midipix__)
+#if !defined(_WIN32) && !defined(MBEDTLS_PLATFORM_IS_UNIXLIKE)
 #error "This module only works on Unix and Windows, see MBEDTLS_TIMING_C in mbedtls_config.h"
 #endif