icu: remove BR2_ARCH_HAS_ATOMICS dependency

The BR2_ARCH_HAS_ATOMICS was added because on ARC, atomic instructions
may not be provided by the architecture and therefore the compiler
does not provide the __sync_*() built-ins.

However, since then, icu was changed and is now able to use C++11
atomics, or even no atomic operations at all. In fact, icu will:

 * If possible, it will use C++11 atomics, which internally rely on
   the __atomic built-ins. These are available since gcc 4.7, and all
   architectures provide it. On some architectures, you *must* link
   with libatomic, on some other architectures, they are available
   built-in, but in all cases, linking against libatomic does not
   harm. Thanks to this, even ARC with no atomic support (which was
   the original reason for adding the BR2_ARCH_HAS_ATOMICS) dependency
   builds fine, provided -latomic is added to LIBS.

 * If C++11 atomics are not available, then it falls back to
   __sync_*() built-ins, which allows compilers older than 4.7 to be
   supported.

 * If really no atomic mechanism is available, then it falls back to a
   basic implementation based on a mutex.

Conclusion:

 - The BR2_ARCH_HAS_ATOMICS dependency is no longer needed.

 - We need to link with -latomic when gcc >= 4.7 is used.

Note that reverse dependencies of icu are also changed accordingly.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/beecrypt/Config.in

@@ -16,7 +16,6 @@ config BR2_PACKAGE_BEECRYPT_CPP
 	depends on BR2_INSTALL_LIBSTDCPP
 	depends on BR2_USE_WCHAR # icu
 	depends on !BR2_BINFMT_FLAT # icu
-	depends on BR2_ARCH_HAS_ATOMICS # icu
 	depends on !BR2_STATIC_LIBS
 	select BR2_PACKAGE_ICU
 	help
@@ -24,7 +23,6 @@ config BR2_PACKAGE_BEECRYPT_CPP
 
 comment "C++ support needs a toolchain w/ C++, wchar, dynamic libraries"
 	depends on !BR2_BINFMT_FLAT
-	depends on BR2_ARCH_HAS_ATOMICS
 	depends on !BR2_INSTALL_LIBSTDCPP || !BR2_USE_WCHAR \
 		|| BR2_STATIC_LIBS
 

package/cppcms/Config.in

@@ -26,7 +26,6 @@ if BR2_PACKAGE_CPPCMS
 config BR2_PACKAGE_CPPCMS_ICU
 	bool "enable icu support"
 	depends on !BR2_BINFMT_FLAT # icu
-	depends on BR2_ARCH_HAS_ATOMICS # icu
 	select BR2_PACKAGE_ICU
 	help
 	  Using ICU allows advanced localization features into CppCMS,

package/icu/Config.in

@@ -7,7 +7,6 @@ config BR2_PACKAGE_ICU
 	# file, and it cannot easily be changed to generate FLAT
 	# format.
 	depends on !BR2_BINFMT_FLAT
-	depends on BR2_ARCH_HAS_ATOMICS
 	help
 	  International Components for Unicode.
 
@@ -28,6 +27,5 @@ endif
 
 comment "icu needs a toolchain w/ C++, wchar, threads"
 	depends on !BR2_BINFMT_FLAT
-	depends on BR2_ARCH_HAS_ATOMICS
 	depends on !BR2_INSTALL_LIBSTDCPP || !BR2_USE_WCHAR || \
 		!BR2_TOOLCHAIN_HAS_THREADS

package/icu/icu.mk

@@ -17,6 +17,14 @@ ICU_CONF_OPTS = \
 	--with-cross-build=$(HOST_ICU_DIR)/source \
 	--disable-samples \
 	--disable-tests
+
+# With gcc >= 4.7, icu prefers to use C++11 atomics, which rely on the
+# __atomic builtins. On certain architectures, this requires linking
+# with libatomic.
+ifeq ($(BR2_TOOLCHAIN_GCC_AT_LEAST_4_7),y)
+ICU_CONF_ENV += LIBS="-latomic"
+endif
+
 HOST_ICU_CONF_OPTS = \
 	--disable-samples \
 	--disable-tests \

package/php/Config.ext

@@ -207,13 +207,11 @@ config BR2_PACKAGE_PHP_EXT_INTL
 	depends on BR2_USE_WCHAR
 	depends on !BR2_BINFMT_FLAT # icu
 	depends on BR2_TOOLCHAIN_HAS_THREADS # icu
-	depends on BR2_ARCH_HAS_ATOMICS # icu
 	help
 	  Internationalization support
 
 comment "intl support needs a toolchain w/ C++, wchar, threads"
 	depends on !BR2_BINFMT_FLAT
-	depends on BR2_ARCH_HAS_ATOMICS
 	depends on !BR2_INSTALL_LIBSTDCPP || !BR2_USE_WCHAR || !BR2_TOOLCHAIN_HAS_THREADS
 
 config BR2_PACKAGE_PHP_EXT_MBSTRING

package/qt-webkit-kiosk/Config.in

@@ -8,7 +8,6 @@ config BR2_PACKAGE_QT_WEBKIT_KIOSK
 	select BR2_PACKAGE_QT5MULTIMEDIA
 	depends on !BR2_STATIC_LIBS # qt5webkit
 	depends on BR2_PACKAGE_QT5_JSCORE_AVAILABLE # qt5webkit
-	depends on BR2_ARCH_HAS_ATOMICS # qt5webkit
 	depends on !BR2_BINFMT_FLAT # qt5webkit
 	help
 	  Simple kiosk-mode browser powered by Qt5Webkit

package/qt5/qt5base/Config.in

@@ -259,7 +259,6 @@ config BR2_PACKAGE_QT5BASE_DBUS
 config BR2_PACKAGE_QT5BASE_ICU
 	bool "Enable ICU support"
 	select BR2_PACKAGE_ICU
-	depends on BR2_ARCH_HAS_ATOMICS # icu
 	depends on !BR2_BINFMT_FLAT # icu
 	help
 	  This option enables ICU support in Qt5. This is for example

package/qt5/qt5webkit/Config.in

@@ -9,7 +9,6 @@ config BR2_PACKAGE_QT5WEBKIT
 	# This module does not support static linking
 	depends on !BR2_STATIC_LIBS
 	depends on BR2_PACKAGE_QT5_JSCORE_AVAILABLE
-	depends on BR2_ARCH_HAS_ATOMICS # icu
 	depends on !BR2_BINFMT_FLAT # icu
 	help
 	  Qt is a cross-platform application and UI framework for