appveyor.yml: exercise build_all_generated.

Reviewed-by: NRichard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5930)

appveyor.yml

@@ -43,7 +43,8 @@ build_script:
     - cd _build
     - ps: >-
         If ($env:Configuration -Match "shared" -or $env:EXTENDED_TESTS) {
-            cmd /c "nmake 2>&1"
+            cmd /c "nmake build_all_generated 2>&1"
+            cmd /c "nmake PERL=no-perl 2>&1"
         }
     - cd ..