fix conditions relating to host_build in non-cross builds

when it comes to compiler flags (be it warnings or include paths), it
doesn't matter whether we building/using bootstrap libraries, but
whether we are actually cross-building.

amends c55bdc271f and d8be8110a.

Change-Id: Idf988107e9cccc486672c0ee70dc9bdf8eab9d8c
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

mkspecs/features/qt_build_extra.prf

@@ -13,7 +13,7 @@ equals(TEMPLATE, subdirs): return()
 
 # It's likely that these extra flags will be wrong for host builds,
 # and the bootstrapped tools usually don't need them anyway.
-host_build:force_bootstrap: return()
+host_build:cross_compile: return()
 
 # The headersclean check needs defines and includes even for
 # header-only modules.

mkspecs/features/qt_common.prf

@@ -44,9 +44,9 @@ contains(TEMPLATE, .*lib) {
     QMAKE_PRL_INSTALL_REPLACE += lib_replace
 }
 
-# The remainder of this file must not apply to bootstrapped tools,
+# The remainder of this file must not apply to host tools/libraries,
 # as the host compiler's version and capabilities are not checked.
-host_build:force_bootstrap: return()
+host_build:cross_compile: return()
 
 warnings_are_errors:warning_clean {
     # If the module declares that it has does its clean-up of warnings, enable -Werror.