[posix] use os defined macros (#5048)

This helps the OT_ASSERT automatically adopt the posix provided assert.

configure.ac

@@ -137,24 +137,17 @@ case ${host_os} in
 
     *darwin*)
         OPENTHREAD_TARGET=darwin
-        OPENTHREAD_TARGET_DEFINES="-DOPENTHREAD_TARGET_DARWIN"
         ;;
 
     *linux*)
         OPENTHREAD_TARGET=linux
-        OPENTHREAD_TARGET_DEFINES="-DOPENTHREAD_TARGET_LINUX"
         ;;
 
 esac
 
-AC_SUBST(OPENTHREAD_TARGET_DARWIN)
 AM_CONDITIONAL([OPENTHREAD_TARGET_DARWIN], [test "${OPENTHREAD_TARGET}" = "darwin"])
-
-AC_SUBST(OPENTHREAD_TARGET_LINUX)
 AM_CONDITIONAL([OPENTHREAD_TARGET_LINUX], [test "${OPENTHREAD_TARGET}" = "linux"])
 
-AC_SUBST(OPENTHREAD_TARGET_DEFINES)
-
 #
 # Checks for build host programs
 #

examples/platforms/gp712/uart-posix.c

@@ -43,13 +43,13 @@
 
 #include "utils/code_utils.h"
 
-#ifdef OPENTHREAD_TARGET_LINUX
+#ifdef __linux__
 #include <sys/prctl.h>
 int   posix_openpt(int oflag);
 int   grantpt(int fildes);
 int   unlockpt(int fd);
 char *ptsname(int fd);
-#endif // OPENTHREAD_TARGET_LINUX
+#endif // __linux__
 
 static uint8_t        s_receive_buffer[128];
 static const uint8_t *s_write_buffer;
@@ -104,7 +104,7 @@ otError otPlatUartEnable(void)
     otError        error = OT_ERROR_NONE;
     struct termios termios;
 
-#ifdef OPENTHREAD_TARGET_LINUX
+#ifdef __linux__
     // Ensure we terminate this process if the
     // parent process dies.
     prctl(PR_SET_PDEATHSIG, SIGHUP);

examples/platforms/simulation/uart.c

@@ -44,13 +44,13 @@
 #include "utils/code_utils.h"
 
 #if OPENTHREAD_SIMULATION_VIRTUAL_TIME_UART == 0
-#ifdef OPENTHREAD_TARGET_LINUX
+#ifdef __linux__
 #include <sys/prctl.h>
 int   posix_openpt(int oflag);
 int   grantpt(int fildes);
 int   unlockpt(int fd);
 char *ptsname(int fd);
-#endif // OPENTHREAD_TARGET_LINUX
+#endif // __linux__
 
 static uint8_t        s_receive_buffer[128];
 static const uint8_t *s_write_buffer;
@@ -83,7 +83,7 @@ otError otPlatUartEnable(void)
     otError        error = OT_ERROR_NONE;
     struct termios termios;
 
-#ifdef OPENTHREAD_TARGET_LINUX
+#ifdef __linux__
     // Ensure we terminate this process if the
     // parent process dies.
     prctl(PR_SET_PDEATHSIG, SIGHUP);

src/core/common/debug.hpp

@@ -41,7 +41,7 @@
 
 #if OPENTHREAD_CONFIG_ASSERT_ENABLE
 
-#if defined(OPENTHREAD_TARGET_DARWIN) || defined(OPENTHREAD_TARGET_LINUX)
+#if defined(__APPLE__) || defined(__linux__)
 
 #include <assert.h>