nuttx: Use text heap for executable memory (#1181)

Based on nuttx patch "Add up_textheap_heapmember":
  https://github.com/apache/incubator-nuttx/pull/6306

core/shared/platform/nuttx/nuttx_platform.c

@@ -6,6 +6,10 @@
 #include "platform_api_extension.h"
 #include "platform_api_vmcore.h"
 
+#if defined(CONFIG_ARCH_USE_TEXT_HEAP)
+#include <nuttx/arch.h>
+#endif
+
 int
 bh_platform_init()
 {
@@ -37,6 +41,12 @@ os_free(void *ptr)
 void *
 os_mmap(void *hint, size_t size, int prot, int flags)
 {
+#if defined(CONFIG_ARCH_USE_TEXT_HEAP)
+    if ((prot & MMAP_PROT_EXEC) != 0) {
+        return up_textheap_memalign(sizeof(void *), size);
+    }
+#endif
+
     if ((uint64)size >= UINT32_MAX)
         return NULL;
     return malloc((uint32)size);
@@ -45,6 +55,12 @@ os_mmap(void *hint, size_t size, int prot, int flags)
 void
 os_munmap(void *addr, size_t size)
 {
+#if defined(CONFIG_ARCH_USE_TEXT_HEAP)
+    if (up_textheap_heapmember(addr)) {
+        up_textheap_free(addr);
+        return;
+    }
+#endif
     return free(addr);
 }