Add qsimd_x86_p.h to the QtCore source tree

Need to collect all header files that belong to the module to make
them visible in CMake source tree. In future commit they will be used
to consider what headers need to be installed for each platform.

Amends 28b4bd7dbb

Change-Id: I7ab4063350254324869d5c2d0ba0f7e336da96fb
Reviewed-by: Jörg Bornemann <joerg.bornemann@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/CMakeLists.txt

@@ -445,6 +445,12 @@ endif()
 #)
 # special case end
 
+qt_internal_extend_target(Core
+    CONDITION ( TEST_architecture_arch STREQUAL i386 ) OR
+        ( TEST_architecture_arch STREQUAL x86_64 )
+    SOURCES
+        global/qsimd_x86_p.h
+)
 qt_internal_extend_target(Core CONDITION ANDROID
     SOURCES
         kernel/qsharedmemory_android.cpp