Edit: /usr/share/dpkg/buildflags.mk (1590B)
# This Makefile snippet defines the following variables:
#
# CFLAGS: flags for the C compiler
# CPPFLAGS: flags for the C preprocessor
# CXXFLAGS: flags for the C++ compiler
# OBJCFLAGS: flags for the Objective C compiler
# OBJCXXFLAGS: flags for the Objective C++ compiler
# GCJFLAGS: flags for the GNU Java compiler
# FFLAGS: flags for the Fortran 77 compiler
# FCFLAGS: flags for the Fortran 9x compiler
# LDFLAGS: flags for the linker
#
# You can also export them in the environment by setting
# DPKG_EXPORT_BUILDFLAGS to a non-empty value.
#
# This list is kept in sync with the default set of flags returned
# by dpkg-buildflags.
dpkg_lazy_eval ?= $$(or $$(value DPKG_CACHE_$(1)),$$(eval DPKG_CACHE_$(1) := $$(shell $(2)))$$(value DPKG_CACHE_$(1)))
DPKG_BUILDFLAGS_LIST = CFLAGS CPPFLAGS CXXFLAGS OBJCFLAGS OBJCXXFLAGS \
GCJFLAGS FFLAGS FCFLAGS LDFLAGS
define dpkg_buildflags_export_envvar
ifdef $(1)
DPKG_BUILDFLAGS_EXPORT_ENVVAR += $(1)="$$(value $(1))"
endif
endef
$(eval $(call dpkg_buildflags_export_envvar,DEB_BUILD_OPTIONS))
$(eval $(call dpkg_buildflags_export_envvar,DEB_BUILD_MAINT_OPTIONS))
$(foreach flag,$(DPKG_BUILDFLAGS_LIST),\
$(foreach operation,SET STRIP APPEND PREPEND,\
$(eval $(call dpkg_buildflags_export_envvar,DEB_$(flag)_MAINT_$(operation)))))
dpkg_buildflags_setvar = $(1) = $(call dpkg_lazy_eval,$(1),$(DPKG_BUILDFLAGS_EXPORT_ENVVAR) dpkg-buildflags --get $(1))
$(foreach flag,$(DPKG_BUILDFLAGS_LIST),\
$(eval $(call dpkg_buildflags_setvar,$(flag))))
ifdef DPKG_EXPORT_BUILDFLAGS
export $(DPKG_BUILDFLAGS_LIST)
endif