Select the proper sources for Windows native runtimes

With the separate Linux source profile Windows native targets
use a different set of sources.

Once a source profile for Windows exists this commit should be
reversed.

ref eng/toolchain/bb-runtimes#78

build_rts.py

@@ -283,11 +283,11 @@ def build_configs(target):
         t = X8664Generic()
     # native platforms
     elif target in ("x86-linux", "x86-windows"):
-        t = X86Native()
+        t = X86Native(target)
     elif target in ("x86_64-linux", "x86_64-windows", "x86_64-windows64"):
-        t = X8664Native()
+        t = X8664Native(target)
     elif target in ("aarch64-linux",):
-        t = Aarch64Native()
+        t = Aarch64Native(target)
     # vx7r2cert
     elif target == "aarch64-vx7r2cert":
         t = AArch64Vx7r2Cert()

native/__init__.py

@@ -2,9 +2,14 @@
 
 
 class Native(DFBBTarget):
-    def __init__(self):
+    def __init__(self, target):
         super().__init__()
         self.add_gnat_sources("src/s-macres__native.adb")
+        # Use the bb source of s-textio for Windows as a custom
+        # source profile is not yet supported.
+        # eng/toolchain/bb-runtimes#78
+        if "windows" in target:
+            self.add_gnat_sources("src/s-textio__stdio.adb")
 
     @property
     def target(self):