Revert "druntime: Use WASIp1 directly instead of POSIX emulation"

This reverts commit 21329a1.

Author: QuantumSegfault

druntime/src/core/internal/abort.d

@@ -42,16 +42,31 @@ void abort(scope string msg, scope string filename = __FILE__, size_t line = __L
         }
     }
     else version (WASIp1) {
-        import core.sys.wasi.p1 : CIOVec, fdWrite;
+        // currently depends on wasi-libc being linked in to provide these "syscalls"
+        // TODO: detach this from wasi-libc
+        alias ushort __wasi_errno_t;
+        alias int __wasi_fd_t;
+        alias size_t __wasi_size_t;
+
+        extern(C) struct __wasi_ciovec_t {
+            const(ubyte)* buf;
+            __wasi_size_t buf_len;
+        }
+
+        pragma(mangle, "__wasi_fd_write")
+        extern(C) static __wasi_errno_t
+        __wasi_fd_write(__wasi_fd_t fd,
+                        const __wasi_ciovec_t *iovs,
+                        size_t iovs_len, __wasi_size_t *retptr0) @nogc nothrow;
 
         static void writeStr(scope const(char)[][] m...) @nogc nothrow @trusted
         {
             foreach (s; m) {
-                CIOVec[1] iovecs;
-                size_t bytesWritten;
-                iovecs[0].buf = cast(const(ubyte)*)s.ptr;
-                iovecs[0].bufLen = s.length;
-                cast(void)fdWrite(2, iovecs[], bytesWritten);
+                __wasi_ciovec_t iovec;
+                __wasi_size_t ret;
+                iovec.buf = cast(const(ubyte)*)s.ptr;
+                iovec.buf_len = s.length;
+                cast(void)__wasi_fd_write(2, &iovec, 1, &ret);
             }
         }
     } else version (WASIp2) {