package/libs/zlib: Add option for O3 optimization

Add option to use O3 optimization as not all devices have
space constraints. This option is default using GCC in upstream
but isn't in the CMake makefile for some reason.

Source: https://github.com/madler/zlib/blob/master/configure#L170

Signed-off-by: Daniel Engberg <daniel.engberg.lists@pyret.net>

package/libs/zlib/Config.in

@@ -0,0 +1,11 @@
+menu "Configuration"
+	depends on PACKAGE_zlib
+
+config ZLIB_OPTIMIZE_SPEED
+	bool "Optimize for speed"
+	help
+		This enables additional optimization and 
+		increases performance considerably at 
+		the expense of binary size.
+
+endmenu

package/libs/zlib/Makefile

@@ -19,6 +19,8 @@ PKG_LICENSE:=Zlib
 PKG_LICENSE_FILES:=README
 PKG_CPE_ID:=cpe:/a:gnu:zlib
 
+PKG_CONFIG_DEPENDS:= CONFIG_ZLIB_OPTIMIZE_SPEED
+
 include $(INCLUDE_DIR)/package.mk
 include $(INCLUDE_DIR)/cmake.mk
 
@@ -47,8 +49,16 @@ define Package/zlib-dev/description
  This package includes the development support files.
 endef
 
+define Package/zlib/config
+	source "$(SOURCE)/Config.in"
+endef
+
 TARGET_CFLAGS += $(FPIC)
 
+ifeq ($(CONFIG_ZLIB_OPTIMIZE_SPEED),y)
+	TARGET_CFLAGS := $(filter-out -O%,$(TARGET_CFLAGS)) -O3
+endif
+
 ifneq ($(findstring neon,$(CONFIG_TARGET_OPTIMIZATION)),)
 	CMAKE_OPTIONS += \
 		-DARMv8=ON