perf: Add libunwind only if selected

The depends are totally wrong. libunwind does not work with powerpc and
i386 as it needs glibc.

Instead of duplicating the platforms, just change the dependency.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

package/devel/perf/Makefile

@@ -10,7 +10,7 @@ include $(INCLUDE_DIR)/kernel.mk
 
 PKG_NAME:=perf
 PKG_VERSION:=$(LINUX_VERSION)
-PKG_RELEASE:=2
+PKG_RELEASE:=3
 
 PKG_USE_MIPS16:=0
 PKG_BUILD_PARALLEL:=1
@@ -26,7 +26,7 @@ include $(INCLUDE_DIR)/package.mk
 define Package/perf
   SECTION:=devel
   CATEGORY:=Development
-  DEPENDS:= +libelf +libdw +(mips||mipsel||powerpc||i386||x86_64||arm||aarch64):libunwind +libpthread +librt +objdump @!IN_SDK @!TARGET_arc770 @KERNEL_PERF_EVENTS
+  DEPENDS:= +libelf +libdw +PACKAGE_libunwind:libunwind +libpthread +librt +objdump @!IN_SDK @!TARGET_arc770 @KERNEL_PERF_EVENTS
   TITLE:=Linux performance monitoring tool
   VERSION:=$(LINUX_VERSION)-$(PKG_RELEASE)
   URL:=http://www.kernel.org