clarify the windows setup a bit

file-selection for compiler-rt_win-64 was not broken (conda understands
forward slashes), but intent is hopefully clearer now (no "Library\" on win).

recipe/bld.bat

@@ -31,5 +31,9 @@ if %ERRORLEVEL% neq 0 exit 1
 cmake --install .
 if %ERRORLEVEL% neq 0 exit 1
 
+:: Also install into %PREFIX%\lib (!= %PREFIX%\Library\lib, the default on win)
+:: because compiler-rt_win-64 is noarch and needs to be installable on linux,
+:: where we don't want the "\Library"; aside from removing that directory,
+:: the paths are the same. Separation into proper outputs happens in the recipe.
 mkdir %PREFIX%\lib\clang\%PKG_VERSION%\lib\windows
 copy %INSTALL_PREFIX%\lib\windows\* %PREFIX%\lib\clang\%PKG_VERSION%\lib\windows\

recipe/meta.yaml

@@ -47,7 +47,9 @@ outputs:
       run_constrained:
         - compiler-rt {{ version }}
     files:
-      - lib/clang/{{ prod_ver }}/lib
+      - lib/clang/{{ prod_ver }}/lib    # [unix]
+      # avoid "Library\" for noarch output
+      - lib\clang\{{ prod_ver }}\lib    # [win]
     test:
       commands:
         - echo {{ MACOSX_DEPLOYMENT_TARGET|default("10.9") }}
@@ -66,6 +68,7 @@ outputs:
     files:
       - lib/clang/{{ prod_ver }}/share             # [unix]
       - lib/clang/{{ prod_ver }}/include           # [unix]
+      # standard windows layout for arch-specific output
       - Library\lib\clang\{{ prod_ver }}\share     # [win]
       - Library\lib\clang\{{ prod_ver }}\include   # [win]
       - Library\lib\clang\{{ prod_ver }}\lib       # [win]