qga: fix missing static and prototypes windows warnings

Reported by clang++, but not by g++.

../qga/vss-win32/provider.cpp:48:6: error: no previous prototype for function 'LockModule' [-Werror,-Wmissing-prototypes]
   48 | void LockModule(BOOL lock)
      |      ^
../qga/vss-win32/provider.cpp:48:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
   48 | void LockModule(BOOL lock)
      | ^
      | static
../qga/vss-win32/provider.cpp:531:13: error: no previous prototype for function 'DllMain' [-Werror,-Wmissing-prototypes]
  531 | BOOL WINAPI DllMain(HINSTANCE hinstDll, DWORD dwReason, LPVOID lpReserved)
      |             ^
../qga/vss-win32/provider.cpp:531:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
  531 | BOOL WINAPI DllMain(HINSTANCE hinstDll, DWORD dwReason, LPVOID lpReserved)
      | ^
      | static

Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Konstantin Kostiuk <kkostiuk@redhat.com>
Link: https://lore.kernel.org/r/20241031040426.772604-7-pierrick.bouvier@linaro.org
Signed-off-by: Konstantin Kostiuk <kkostiuk@redhat.com>

qga/vss-win32/install.cpp

@@ -39,7 +39,7 @@ const GUID CLSID_WbemLocator = { 0x4590f811, 0x1d3a, 0x11d0,
 const GUID IID_IWbemLocator = { 0xdc12a687, 0x737f, 0x11cf,
     {0x88, 0x4d, 0x00, 0xaa, 0x00, 0x4b, 0x2e, 0x24} };
 
-void errmsg(DWORD err, const char *text)
+static void errmsg(DWORD err, const char *text)
 {
     /*
      * `text' contains function call statement when errmsg is called via chk().
@@ -242,6 +242,7 @@ out:
 }
 
 /* Unregister this module from COM+ Applications Catalog */
+STDAPI COMUnregister(void);
 STDAPI COMUnregister(void)
 {
     qga_debug_begin;
@@ -256,6 +257,7 @@ out:
 }
 
 /* Register this module to COM+ Applications Catalog */
+STDAPI COMRegister(void);
 STDAPI COMRegister(void)
 {
     qga_debug_begin;
@@ -380,11 +382,13 @@ out:
     return hr;
 }
 
+STDAPI_(void) CALLBACK DLLCOMRegister(HWND, HINSTANCE, LPSTR, int);
 STDAPI_(void) CALLBACK DLLCOMRegister(HWND, HINSTANCE, LPSTR, int)
 {
     COMRegister();
 }
 
+STDAPI_(void) CALLBACK DLLCOMUnregister(HWND, HINSTANCE, LPSTR, int);
 STDAPI_(void) CALLBACK DLLCOMUnregister(HWND, HINSTANCE, LPSTR, int)
 {
     COMUnregister();

qga/vss-win32/provider.cpp

@@ -45,7 +45,7 @@ const IID IID_IVssEnumObject = { 0xAE1C7110, 0x2F60, 0x11d3,
     {0x8A, 0x39, 0x00, 0xC0, 0x4F, 0x72, 0xD8, 0xE3} };
 
 
-void LockModule(BOOL lock)
+static void LockModule(BOOL lock)
 {
     if (lock) {
         InterlockedIncrement(&g_nComObjsInUse);
@@ -527,6 +527,9 @@ STDAPI DllCanUnloadNow()
     return g_nComObjsInUse == 0 ? S_OK : S_FALSE;
 }
 
+EXTERN_C
+BOOL WINAPI DllMain(HINSTANCE hinstDll, DWORD dwReason, LPVOID lpReserved);
+
 EXTERN_C
 BOOL WINAPI DllMain(HINSTANCE hinstDll, DWORD dwReason, LPVOID lpReserved)
 {

qga/vss-win32/requester.cpp

@@ -254,8 +254,8 @@ out:
     qga_debug_end;
 }
 
-DWORD get_reg_dword_value(HKEY baseKey, LPCSTR subKey, LPCSTR valueName,
-                          DWORD defaultData)
+static DWORD get_reg_dword_value(HKEY baseKey, LPCSTR subKey, LPCSTR valueName,
+                                 DWORD defaultData)
 {
     qga_debug_begin;
 
@@ -272,12 +272,12 @@ DWORD get_reg_dword_value(HKEY baseKey, LPCSTR subKey, LPCSTR valueName,
     return dwordData;
 }
 
-bool is_valid_vss_backup_type(VSS_BACKUP_TYPE vssBT)
+static bool is_valid_vss_backup_type(VSS_BACKUP_TYPE vssBT)
 {
     return (vssBT > VSS_BT_UNDEFINED && vssBT < VSS_BT_OTHER);
 }
 
-VSS_BACKUP_TYPE get_vss_backup_type(
+static VSS_BACKUP_TYPE get_vss_backup_type(
     VSS_BACKUP_TYPE defaultVssBT = DEFAULT_VSS_BACKUP_TYPE)
 {
     qga_debug_begin;