VS: Map /Y- flag to not use precompiled headers with VS 2008

Source/cmGlobalVisualStudio7Generator.cxx

@@ -37,6 +37,7 @@ static cmVS7FlagTable cmVS7ExtraFlagTable[] = {
     cmVS7FlagTable::UserValueIgnored | cmVS7FlagTable::Continue },
   { "PrecompiledHeaderThrough", "Yu", "Precompiled Header Name", "",
     cmVS7FlagTable::UserValueRequired },
+  { "UsePrecompiledHeader", "Y-", "Don't use precompiled header", "0", 0 },
   { "WholeProgramOptimization", "LTCG", "WholeProgramOptimization", "true",
     0 },
 

Source/cmGlobalVisualStudio8Generator.cxx

@@ -370,6 +370,7 @@ static cmVS7FlagTable cmVS8ExtraFlagTable[] = {
     cmVS7FlagTable::UserValueIgnored | cmVS7FlagTable::Continue },
   { "PrecompiledHeaderThrough", "Yu", "Precompiled Header Name", "",
     cmVS7FlagTable::UserValueRequired },
+  { "UsePrecompiledHeader", "Y-", "Don't use precompiled header", "0", 0 },
   // There is no YX option in the VS8 IDE.
 
   // Exception handling mode.  If no entries match, it will be FALSE.

Source/cmLocalVisualStudio7Generator.cxx

@@ -402,6 +402,7 @@ cmVS7FlagTable cmLocalVisualStudio7GeneratorFlagTable[] = {
     cmVS7FlagTable::UserValueIgnored | cmVS7FlagTable::Continue },
   { "PrecompiledHeaderThrough", "Yc", "Precompiled Header Name", "",
     cmVS7FlagTable::UserValueRequired },
+  { "UsePrecompiledHeader", "Y-", "Don't use precompiled header", "0", 0 },
   { "PrecompiledHeaderFile", "Fp", "Generated Precompiled Header", "",
     cmVS7FlagTable::UserValue },
   // The YX and Yu options are in a per-global-generator table because