depends: build Boost with -std=c++17

depends/packages/boost.mk

@@ -27,7 +27,7 @@ ifneq (,$(findstring clang,$($(package)_cxx)))
 endif
 $(package)_archiver_$(host_os)=$($(package)_ar)
 $(package)_config_libraries=filesystem,system,thread,test
-$(package)_cxxflags=-std=c++11 -fvisibility=hidden
+$(package)_cxxflags=-std=c++17 -fvisibility=hidden
 $(package)_cxxflags_linux=-fPIC
 $(package)_cxxflags_android=-fPIC
 endef