appveyor.yml: Let 'nmake' run by defaut silently (/S), using MAKEVERBOSE like .travis.yml

Reviewed-by: NMatt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/13580)

appveyor.yml

@@ -50,13 +50,19 @@ before_build:
                  Select-String "\[extended tests\]") ) {
             $env:EXTENDED_TESTS="yes"
         }
+    - ps: >-
+        If ($env:BUILDONLY -or $env:MAKEVERBOSE) {
+            $env:NMAKE="nmake"
+        } Else {
+            $env:NMAKE="nmake /S"
+        }
 
 build_script:
     - cd _build
     - ps: >-
         If ($env:Configuration -Match "shared" -or $env:EXTENDED_TESTS) {
-            cmd /c "nmake build_all_generated 2>&1"
-            cmd /c "nmake PERL=no-perl 2>&1"
+            cmd /c "%NMAKE% build_all_generated 2>&1"
+            cmd /c "%NMAKE% PERL=no-perl 2>&1"
         }
     - cd ..
 
@@ -65,14 +71,14 @@ test_script:
     - ps: >-
         If ($env:Configuration -Match "shared" -or $env:EXTENDED_TESTS) {
             if ($env:EXTENDED_TESTS) {
-                cmd /c "nmake test HARNESS_VERBOSE_FAILURE=yes 2>&1"
+                cmd /c "%NMAKE% test HARNESS_VERBOSE_FAILURE=yes 2>&1"
             } Else {
-                cmd /c "nmake test HARNESS_VERBOSE_FAILURE=yes TESTS=-test_fuzz 2>&1"
+                cmd /c "%NMAKE% test HARNESS_VERBOSE_FAILURE=yes TESTS=-test_fuzz 2>&1"
             }
         }
     - ps: >-
         if ($env:EXTENDED_TESTS) {
             mkdir ..\_install
-            cmd /c "nmake install DESTDIR=..\_install 2>&1"
+            cmd /c "%NMAKE% install DESTDIR=..\_install 2>&1"
         }
     - cd ..