Remove whole sys-include folder when cross-compiler has been built.

* at least for gcc2, we used to leave the 'os' subfolder in there,
  which may have caused problems when Haiku's headers have changed
  since the last time the compiler was built.
(cherry picked from commit 92bb2fb33e)

build/scripts/build_cross_tools

@@ -189,8 +189,7 @@ rm -f $installDir/lib/gcc-lib/i586-pc-haiku/$haikuRequiredLegacyGCCVersion/inclu
 
 # remove the system headers from the installation dir
 # Only the ones from the source tree should be used.
-sysIncludeDir=$installDir/i586-pc-haiku/sys-include
-rm -rf $sysIncludeDir/be $sysIncludeDir/posix
+rm -rf $installDir/i586-pc-haiku/sys-include
 
 # remove the objects dir
 rm -rf $objDir

build/scripts/build_cross_tools_gcc4

@@ -247,8 +247,7 @@ fi
 
 # remove the system headers from the installation dir
 # Only the ones from the source tree should be used.
-sysIncludeDir=$installDir/$haikuMachine/sys-include
-rm -rf $sysIncludeDir/os $sysIncludeDir/posix
+rm -rf $installDir/$haikuMachine/sys-include
 
 # remove the objects dir
 rm -rf $objDir