treewide: add support for "gc-sections" in PKG_BUILD_FLAGS

This reduces open coding and allows to easily add a knob to
enable it treewide, where chosen packages can still opt-out via
"no-gc-sections".

Note: libnl, mbedtls and opkg only used the CFLAGS part without the
LDFLAGS counterpart. That doesn't help at all if the goal is to produce
smaller binaries. I consider that an accident, and this fixes it.

Note: there are also packages using only the LDFLAGS part. I didn't
touch those, as gc might have been disabled via CFLAGS intentionally.

Signed-off-by: Andre Heider <a.heider@gmail.com>

package/network/utils/iproute2/Makefile

@@ -19,6 +19,8 @@ PKG_BUILD_DEPENDS:=iptables
 PKG_LICENSE:=GPL-2.0
 PKG_CPE_ID:=cpe:/a:iproute2_project:iproute2
 
+PKG_BUILD_FLAGS:=gc-sections
+
 include $(INCLUDE_DIR)/kernel.mk
 include $(INCLUDE_DIR)/package.mk
 include $(INCLUDE_DIR)/nls.mk
@@ -171,8 +173,8 @@ define Build/Configure
 		> $(PKG_BUILD_DIR)/include/SNAPSHOT.h
 endef
 
-TARGET_CFLAGS += -ffunction-sections -fdata-sections -flto
-TARGET_LDFLAGS += -Wl,--gc-sections -Wl,--as-needed
+TARGET_CFLAGS += -flto
+TARGET_LDFLAGS += -Wl,--as-needed
 TARGET_CPPFLAGS += -I$(STAGING_DIR)/usr/include/libnl-tiny
 
 MAKE_FLAGS += \

package/network/utils/iptables/Makefile

@@ -20,6 +20,7 @@ PKG_FIXUP:=autoreconf
 PKG_FLAGS:=nonshared
 
 PKG_INSTALL:=1
+PKG_BUILD_FLAGS:=gc-sections
 PKG_BUILD_PARALLEL:=1
 PKG_LICENSE:=GPL-2.0
 PKG_CPE_ID:=cpe:/a:netfilter_core_team:iptables
@@ -591,12 +592,8 @@ TARGET_CPPFLAGS := \
 TARGET_CFLAGS += \
 	-I$(PKG_BUILD_DIR)/include \
 	-I$(LINUX_DIR)/user_headers/include \
-	-ffunction-sections -fdata-sections \
 	-DNO_LEGACY
 
-TARGET_LDFLAGS += \
-	-Wl,--gc-sections
-
 CONFIGURE_ARGS += \
 	--enable-shared \
 	--enable-static \

package/network/utils/iw/Makefile

@@ -18,6 +18,8 @@ PKG_HASH:=f167bbe947dd53bb9ebc0c1dcef5db6ad73ac1d6084f2c6f9376c5c360cc4d4e
 PKG_MAINTAINER:=Felix Fietkau <nbd@nbd.name>
 PKG_LICENSE:=GPL-2.0
 
+PKG_BUILD_FLAGS:=gc-sections
+
 include $(INCLUDE_DIR)/package.mk
 
 define Package/iw
@@ -55,8 +57,8 @@ ifeq ($(BUILD_VARIANT),full)
 endif
 
 MAKE_FLAGS += \
-	CFLAGS="$(TARGET_CPPFLAGS) $(TARGET_CFLAGS) -ffunction-sections -fdata-sections" \
-	LDFLAGS="$(TARGET_LDFLAGS) -Wl,--gc-sections -flto" \
+	CFLAGS="$(TARGET_CPPFLAGS) $(TARGET_CFLAGS)" \
+	LDFLAGS="$(TARGET_LDFLAGS) -flto" \
 	NL1FOUND="" NL2FOUND=Y \
 	NLLIBNAME="libnl-tiny" \
 	LIBS="-lm -lnl-tiny" \

package/network/utils/tcpdump/Makefile

@@ -20,6 +20,7 @@ PKG_LICENSE:=BSD-3-Clause
 PKG_CPE_ID:=cpe:/a:tcpdump:tcpdump
 
 PKG_INSTALL:=1
+PKG_BUILD_FLAGS:=gc-sections
 PKG_BUILD_PARALLEL:=1
 
 include $(INCLUDE_DIR)/package.mk
@@ -48,9 +49,6 @@ CONFIGURE_ARGS += \
 	--without-crypto \
 	$(call autoconf_bool,CONFIG_IPV6,ipv6)
 
-TARGET_CFLAGS += -ffunction-sections -fdata-sections
-TARGET_LDFLAGS += -Wl,--gc-sections
-
 ifeq ($(BUILD_VARIANT),mini)
   TARGET_CFLAGS += -DTCPDUMP_MINI
   CONFIGURE_ARGS += --disable-smb

package/network/utils/umbim/Makefile

@@ -14,6 +14,7 @@ PKG_LICENSE:=GPL-2.0
 PKG_LICENSE_FILES:=
 
 PKG_FLAGS:=nonshared
+PKG_BUILD_FLAGS:=gc-sections
 
 include $(INCLUDE_DIR)/package.mk
 include $(INCLUDE_DIR)/cmake.mk
@@ -32,9 +33,7 @@ define Package/umbim/description
 endef
 
 TARGET_CFLAGS += \
-	-I$(STAGING_DIR)/usr/include -ffunction-sections -fdata-sections
-
-TARGET_LDFLAGS += -Wl,--gc-sections
+	-I$(STAGING_DIR)/usr/include
 
 define Package/umbim/install
 	$(INSTALL_DIR) $(1)/sbin

package/network/utils/uqmi/Makefile

@@ -14,6 +14,7 @@ PKG_LICENSE:=GPL-2.0
 PKG_LICENSE_FILES:=
 
 PKG_FLAGS:=nonshared
+PKG_BUILD_FLAGS:=gc-sections
 
 include $(INCLUDE_DIR)/package.mk
 include $(INCLUDE_DIR)/cmake.mk
@@ -33,13 +34,9 @@ endef
 
 TARGET_CFLAGS += \
 	-I$(STAGING_DIR)/usr/include \
-	-ffunction-sections \
-	-fdata-sections \
 	-Wno-error=dangling-pointer \
 	-Wno-error=maybe-uninitialized
 
-TARGET_LDFLAGS += -Wl,--gc-sections
-
 CMAKE_OPTIONS += \
 	-DDEBUG=1