build: add ATOMIC64_DEPENDS

Packages that use 64-bit atomics carry open-coded architecture lists
such as +(arm||armeb||mips||mipsel||powerpc):libatomic. Those lists
drift (ruby still names arc), over-include ARMv6K and ARMv7 targets
whose compiler inlines 64-bit atomics via ldrexd/strexd, and
under-include ARMv5 in other packages. Add HAS_ATOMIC64, selected on
the architectures where GCC emits 64-bit atomics inline (all 64-bit
ones, x86 via cmpxchg8b, ARMv6K and ARMv7), and ATOMIC64_DEPENDS as
the single dependency expression to use instead. The condition is one
negated symbol because the Depends: evaluator in package-pack.mk only
handles flat conjunctions and disjunctions. 16-byte and size-generic
atomics need libatomic on every architecture and keep a plain
+libatomic dependency.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

include/package.mk

@@ -71,6 +71,8 @@ else
   TARGET_LDFLAGS += -zmax-page-size=4096
 endif
 
+ATOMIC64_DEPENDS:=+!HAS_ATOMIC64:libatomic
+
 include $(INCLUDE_DIR)/hardening.mk
 include $(INCLUDE_DIR)/prereq.mk
 include $(INCLUDE_DIR)/unpack.mk

target/Config.in

@@ -116,7 +116,11 @@ config NAND_SUPPORT
 config LEGACY_SDCARD_SUPPORT
 	bool
 
+config HAS_ATOMIC64
+	bool
+
 config ARCH_64BIT
+	select HAS_ATOMIC64
 	bool
 
 config VIRTIO_SUPPORT
@@ -153,16 +157,20 @@ config arm_v6
 	bool
 
 config arm_v6k
+	select HAS_ATOMIC64
 	bool
 
 config arm_v7
+	select HAS_ATOMIC64
 	bool
 
 config i386
+	select HAS_ATOMIC64
 	bool
 
 config i686
-	bool 
+	select HAS_ATOMIC64
+	bool
 
 config loongarch64
 	select ARCH_64BIT