Allow to customize build flags to pass for each platform

Because some platforms may required to disable some flags, this
allow to control which flags are passed for each platform.

debian/rules

@@ -3,17 +3,24 @@
 include /usr/share/dpkg/architecture.mk
 include /usr/share/dpkg/buildtools.mk
 
-export DEB_BUILD_MAINT_OPTIONS = hardening=+all,-relro,-stackprotector,-format
+export DEB_BUILD_MAINT_OPTIONS = hardening=+all
+
 export CFG_USER_TA_TARGETS = ta_arm64
 
 platforms := k3-am62x vexpress-qemu_armv8a
 
 # k3 platform
-k3-am62x_DEB_BUILD_MAINT_OPTIONS = hardening=+all,-relro
+k3-am62x_CFLAGS = $(shell DEB_BUILD_MAINT_OPTIONS=hardening=+all,-relro dpkg-buildflags --get CFLAGS)
+k3-am62x_CPPFLAGS = $(shell DEB_BUILD_MAINT_OPTIONS=hardening=+all,-relro dpkg-buildflags --get CPPFLAGS)
+k3-am62x_CXXFLAGS = $(shell DEB_BUILD_MAINT_OPTIONS=hardening=+all,-relro dpkg-buildflags --get CXXFLAGS)
+k3-am62x_LDFLAGS = $(shell DEB_BUILD_MAINT_OPTIONS=hardening=+all,-relro dpkg-buildflags --get LDFLAGS)
 k3-am62x_assigns := O=out/arm-plat-k3 CFG_ARM64_core=y
 
 # qemu platform as non debug
-vexpress-qemu_armv8a_DEB_BUILD_MAINT_OPTIONS = hardening=+all,-relro,-stackprotector,-format
+vexpress-qemu_armv8a_CFLAGS = $(shell DEB_BUILD_MAINT_OPTIONS=hardening=+all,-relro,-stackprotector,-format dpkg-buildflags --get CFLAGS)
+vexpress-qemu_armv8a_CPPFLAGS = $(shell DEB_BUILD_MAINT_OPTIONS=hardening=+all,-relro,-stackprotector,-format dpkg-buildflags --get CPPFLAGS)
+vexpress-qemu_armv8a_CXXFLAGS = $(shell DEB_BUILD_MAINT_OPTIONS=hardening=+all,-relro,-stackprotector,-format dpkg-buildflags --get CXXFLAGS)
+vexpress-qemu_armv8a_LDFLAGS = $(shell DEB_BUILD_MAINT_OPTIONS=hardening=+all,-relro,-stackprotector,-format dpkg-buildflags --get LDFLAGS)
 vexpress-qemu_armv8a_subplatforms := vexpress-qemu_armv8a_non-virt vexpress-qemu_armv8a_virt
 vexpress-qemu_armv8a_non-virt_assigns := O=out/arm-plat-vexpress             CFG_TEE_CORE_LOG_LEVEL=3 CFG_TEE_BENCHMARK=n CFG_ARM_GICV3=y CFG_ARM64_core=y CFG_VIRTUALIZATION=n
 vexpress-qemu_armv8a_virt_assigns :=     O=out/arm-plat-vexpress-virtualized CFG_TEE_CORE_LOG_LEVEL=3 CFG_TEE_BENCHMARK=n CFG_ARM_GICV3=y CFG_ARM64_core=y CFG_VIRTUALIZATION=y
@@ -24,6 +31,8 @@ define build_platform
 	$(eval subplatforms := $(if $($(platform)_subplatforms), $($(platform)_subplatforms), $(platform)))
 	$(foreach subplatform, $(subplatforms), \
 		CROSS_COMPILE=aarch64-linux-gnu-  \
+		CFLAGS='$($(platform)_CFLAGS)' CPPFLAGS='$($(platform)_CPPFLAGS)' \
+		CXXFLAGS='$($(platform)_CXXFLAGS)' LDFLAGS='$($(platform)_LDFLAGS)' \
 		make PLATFORM=$(platform) $($(subplatform)_assigns) DEBUG=$(debug) V=1; \
 	)
 endef