Remove src/corelib/arch, merging with src/corelib/thread

There is no more architecture-specific code.

Change-Id: Ie9d9215342d449c48a11fffd151d11411cd73fc7
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

src/corelib/arch/arch.pri

@@ -1,5 +0,0 @@
-HEADERS += \
-    arch/qatomic_bootstrap.h \
-    arch/qatomic_cxx11.h
-
-qtConfig(std-atomic64): QMAKE_USE += libatomic

src/corelib/corelib.pro

@@ -32,7 +32,6 @@ ANDROID_PERMISSIONS = \
 freebsd|openbsd: QMAKE_LFLAGS_NOUNDEF =
 
 include(animation/animation.pri)
-include(arch/arch.pri)
 include(global/global.pri)
 include(thread/thread.pri)
 include(tools/tools.pri)

src/corelib/thread/thread.pri

@@ -10,6 +10,8 @@ HEADERS += thread/qmutex.h \
            thread/qthreadstorage.h \
            thread/qwaitcondition.h \
            thread/qatomic.h \
+           thread/qatomic_bootstrap.h \
+           thread/qatomic_cxx11.h \
            thread/qbasicatomic.h \
            thread/qgenericatomic.h
 
@@ -67,3 +69,5 @@ win32 {
         thread/qthread_unix.cpp \
         thread/qwaitcondition_unix.cpp
 }
+
+qtConfig(std-atomic64): QMAKE_USE += libatomic