Fix the AVX2 logic checks

I derped the check in viewer_mainfest so all builds seemed like AVX to the installer
The weird NSIS DSL also has weird behaviour in the if statements so I've reworked that and also added a "open in new window" for the download page offer.

indra/newview/installers/windows/installer_template.nsi

@@ -178,9 +178,57 @@ Var FRIENDLY_APP_NAME   # <FS:Ansariel> FIRE-30446: Set FriendlyAppName for prot
 Function dirPre
     StrCmp $SKIP_DIALOGS "true" 0 +2
 	Abort
-
 FunctionEnd    
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Open link in a new browser window
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+Function openLinkNewWindow
+  Push $3
+  Exch
+  Push $2
+  Exch
+  Push $1
+  Exch
+  Push $0
+  Exch
+ 
+  ReadRegStr $0 HKCR "http\shell\open\command" ""
+# Get browser path
+    DetailPrint $0
+  StrCpy $2 '"'
+  StrCpy $1 $0 1
+  StrCmp $1 $2 +2 # if path is not enclosed in " look for space as final char
+    StrCpy $2 ' '
+  StrCpy $3 1
+  loop:
+    StrCpy $1 $0 1 $3
+    DetailPrint $1
+    StrCmp $1 $2 found
+    StrCmp $1 "" found
+    IntOp $3 $3 + 1
+    Goto loop
+ 
+  found:
+    StrCpy $1 $0 $3
+    StrCmp $2 " " +2
+      StrCpy $1 '$1"'
+ 
+  Pop $0
+  Exec '$1 $0'
+  Pop $0
+  Pop $1
+  Pop $2
+  Pop $3
+FunctionEnd
+ 
+!macro _OpenURL URL
+Push "${URL}"
+Call openLinkNewWindow
+!macroend
+ 
+!define OpenURL '!insertmacro "_OpenURL"'
+
 ; Add the AVX2 check functions
 Function CheckCPUFlagsAVX2
     Push $1
@@ -188,6 +236,7 @@ Function CheckCPUFlagsAVX2
     IntCmp $1 1 OK_AVX2
     ; AVX2 not supported
     MessageBox MB_OK $(MissingAVX2)
+    ${OpenURL} 'https://www.firestormviewer.org/early-access-beta-downloads-legacy-cpus'
     Quit
 
   OK_AVX2:
@@ -198,23 +247,17 @@ FunctionEnd
 Function CheckCPUFlagsAVX2_Prompt
     Push $1
     System::Call 'kernel32::IsProcessorFeaturePresent(i 40) i .r1'  ; 40 is PF_AVX2_INSTRUCTIONS_AVAILABLE
-    IntCmp $1 1 OK_AVX2 Not_AVX2
-
+    IntCmp $1 1 OK_AVX2 
+    Pop $1
+    Return
   OK_AVX2:
     MessageBox MB_YESNO $(AVX2Available) IDYES DownloadAVX2 IDNO ContinueInstall
     DownloadAVX2:
-      ExecShell open 'https://www.firestormviewer.org/early-access-beta-downloads/'
+      ${OpenURL} 'https://www.firestormviewer.org/early-access-beta-downloads/'
       Quit
     ContinueInstall:
-      Goto End
-
-  Not_AVX2:
-    ; CPU does not support AVX2, continue installation
-    Goto End
-
-  End:
-    Pop $1
-    Return
+      Pop $1
+      Return
 FunctionEnd
 
 # <FS:Ansariel> Optional start menu entry
@@ -260,6 +303,10 @@ ${If} $0 != ""
 ${EndIf}
 
 Call CheckCPUFlags							# Make sure we have SSE2 support
+
+# Two checks here, if we are an AVX2 build we want to abort if no AVX2 support on this CPU.
+# If we are not an AVX2 build but the CPU can support it then we want to prompt them to download the AVX2 version
+# but also allow them to override.
 ${If} ${ISAVX2} == 1
   Call CheckCPUFlagsAVX2
 ${Else}

indra/newview/viewer_manifest.py

@@ -951,7 +951,7 @@ class Windows_x86_64_Manifest(ViewerManifest):
         
         substitution_strings['installer_file'] = installer_file
         substitution_strings['is64bit'] = (1 if (self.address_size == 64) else 0)
-        substitution_strings['isavx2'] = (1 if (self.fs_is_avx2) else 0)
+        substitution_strings['isavx2'] = (1 if (self.fs_is_avx2()) else 0)
         substitution_strings['is_opensim'] = self.fs_is_opensim() # <FS:Ansariel> FIRE-30446: Register hop-protocol for OS version only
         substitution_strings['friendly_app_name'] = self.friendly_app_name() # <FS:Ansariel> FIRE-30446: Set FriendlyAppName for protocol registrations
         substitution_strings['icon_suffix'] = ("_os" if (self.fs_is_opensim()) else "") # <FS:Ansariel> FIRE-24335: Use different icon for OpenSim version