win: fix custom actions for WiX older than 3.9

This is a port of e192f61514 .

Original commit message:

  Older WiX versions included a header with extern "C" declaration,
  hence the custom action source must be C++.

  Reviewed-By: João Reis <reis@janeasystems.com>
  PR-URL: https://github.com/joyent/node/pull/25569

PR-URL: https://github.com/nodejs/node/pull/2843
Reviewed-By: rvagg - Rod Vagg <rod@vagg.org>
Reviewed-By: orangemocha - Alexis Campailla <orangemocha@nodejs.org>
Reviewed-By: bnoordhuis - Ben Noordhuis <info@bnoordhuis.nl>

tools/msvs/msi/custom_actions.cc

@@ -7,7 +7,7 @@
 #define GUID_BUFFER_SIZE 39 // {8-4-4-4-12}\0
 
 
-UINT WINAPI SetInstallScope(MSIHANDLE hInstall) {
+extern "C" UINT WINAPI SetInstallScope(MSIHANDLE hInstall) {
   HRESULT hr = S_OK;
   UINT er = ERROR_SUCCESS;
   TCHAR upgrade_code[GUID_BUFFER_SIZE];
@@ -56,7 +56,7 @@ LExit:
 }
 
 
-UINT WINAPI BroadcastEnvironmentUpdate(MSIHANDLE hInstall) {
+extern "C" UINT WINAPI BroadcastEnvironmentUpdate(MSIHANDLE hInstall) {
   HRESULT hr = S_OK;
   UINT er = ERROR_SUCCESS;
 
@@ -77,7 +77,7 @@ LExit:
 }
 
 
-BOOL WINAPI DllMain(HINSTANCE hInst, ULONG ulReason, VOID* dummy) {
+extern "C" BOOL WINAPI DllMain(HINSTANCE hInst, ULONG ulReason, VOID* dummy) {
   switch (ulReason) {
     case DLL_PROCESS_ATTACH:
       WcaGlobalInitialize(hInst);

tools/msvs/msi/custom_actions.vcxproj

@@ -169,7 +169,7 @@
     </Link>
   </ItemDefinitionGroup>
   <ItemGroup>
-    <ClCompile Include="custom_actions.c">
+    <ClCompile Include="custom_actions.cc">
     </ClCompile>
   </ItemGroup>
   <ItemGroup>