add memcpy impl to builtins

crates/compiler/builtins/bitcode/src/libc.zig

@@ -0,0 +1,41 @@
+const std = @import("std");
+const builtin = @import("builtin");
+const arch = builtin.cpu.arch;
+
+comptime {
+    @export(memcpy, .{ .name = "roc_memcpy", .linkage = .Weak });
+    @export(memcpy, .{ .name = "memcpy", .linkage = .Weak });
+}
+
+const Memcpy = fn (noalias [*]u8, noalias [*]const u8, len: usize) callconv(.C) [*]u8;
+
+pub var memcpy_target: Memcpy = switch (arch) {
+    .x86_64 => memcpy,
+    else => unreachable,
+};
+
+pub fn memcpy(noalias dest: [*]u8, noalias src: [*]const u8, len: usize) callconv(.C) [*]u8 {
+    switch (arch) {
+        .x86_64 => {
+            @memcpy(dest, src, len);
+            return memcpy_target(dest, src, len);
+        },
+        .i386 => {
+            @memcpy(dest, src, len);
+            return dest;
+        },
+        .aarch64 => {
+            @memcpy(dest, src, len);
+            return dest;
+        },
+        .arm => {
+            @memcpy(dest, src, len);
+            return dest;
+        },
+        .wasm32 => {
+            @memcpy(dest, src, len);
+            return dest;
+        },
+        else => @compileError("Unsupported architecture for memcpy"),
+    }
+}

crates/compiler/builtins/bitcode/src/main.zig

@@ -7,6 +7,7 @@ const panic_utils = @import("panic.zig");
 
 comptime {
     _ = @import("compiler_rt.zig");
+    _ = @import("libc.zig");
 }
 
 const ROC_BUILTINS = "roc_builtins";