Add visualizer for OsString and fixup other string visualizers

src/etc/natvis/intrinsic.natvis

@@ -1,8 +1,8 @@
 <?xml version="1.0" encoding="utf-8"?>
 <AutoVisualizer xmlns="http://schemas.microsoft.com/vstudio/debugger/natvis/2010">
   <Type Name="str">
-    <DisplayString>{data_ptr,[length]s8}</DisplayString>
-    <StringView>data_ptr,[length]s8</StringView>
+    <DisplayString>{(char*)data_ptr,[length]s8}</DisplayString>
+    <StringView>(char*)data_ptr,[length]s8</StringView>
     <Expand>
       <Item Name="[len]" ExcludeView="simple">length</Item>
       <Synthetic Name="[chars]">

src/etc/natvis/libstd.natvis

@@ -74,7 +74,7 @@
   </Type>
 
   <Type Name="std::ffi::c_str::CString">
-    <DisplayString>{inner.data_ptr,s}</DisplayString>
+    <DisplayString>{(char*)inner.data_ptr}</DisplayString>
     <Expand>
       <Synthetic Name="[chars]">
         <Expand>
@@ -101,4 +101,18 @@
       </Synthetic>
     </Expand>
   </Type>
+
+  <Type Name="std::ffi::os_str::OsString">
+    <DisplayString>{(char*)inner.inner.bytes.buf.ptr.pointer,[inner.inner.bytes.len]}</DisplayString>
+    <Expand>
+      <Synthetic Name="[chars]">
+        <Expand>
+          <ArrayItems>
+            <Size>inner.inner.bytes.len</Size>
+            <ValuePointer>(char*)inner.inner.bytes.buf.ptr.pointer</ValuePointer>
+          </ArrayItems>
+        </Expand>
+      </Synthetic>
+    </Expand>
+  </Type>
 </AutoVisualizer>

src/test/debuginfo/pretty-std.rs

@@ -111,8 +111,9 @@
 // cdb-check:    [11]             : 33 '!' [Type: char]
 
 // cdb-command: dx os_string
-// cdb-check:os_string        [Type: [...]::OsString]
-// NOTE: OsString doesn't have a .natvis entry yet.
+// cdb-check:os_string        : "IAMA OS string 😃" [Type: std::ffi::os_str::OsString]
+// cdb-check:    [<Raw View>]     [Type: std::ffi::os_str::OsString]
+// cdb-check:    [chars]
 
 // cdb-command: dx some
 // cdb-check:some             : Some [Type: enum$<core::option::Option<i16> >]