build: add and use CXX_STANDARD in depends

depends/Makefile

@@ -46,6 +46,7 @@ LTO ?=
 FALLBACK_DOWNLOAD_PATH ?= https://bitcoincore.org/depends-sources
 
 C_STANDARD ?= c11
+CXX_STANDARD ?= c++17
 
 BUILD = $(shell ./config.guess)
 HOST ?= $(BUILD)

depends/README.md

@@ -97,6 +97,7 @@ The following can be set when running make: `make FOO=bar`
 - `SDK_PATH`: Path where SDKs can be found (used by macOS)
 - `FALLBACK_DOWNLOAD_PATH`: If a source file can't be fetched, try here before giving up
 - `C_STANDARD`: Set the C standard version used. Defaults to `c11`.
+- `CXX_STANDARD`: Set the C++ standard version used. Defaults to `c++17`.
 - `NO_QT`: Don't download/build/cache Qt and its dependencies
 - `NO_QR`: Don't download/build/cache packages needed for enabling qrencode
 - `NO_ZMQ`: Don't download/build/cache packages needed for enabling ZeroMQ

depends/hosts/android.mk

@@ -7,6 +7,7 @@ android_CC=$(ANDROID_TOOLCHAIN_BIN)/$(HOST)$(ANDROID_API_LEVEL)-clang
 endif
 
 android_CFLAGS=-std=$(C_STANDARD)
+android_CXXFLAGS=-std=$(CXX_STANDARD)
 
 ifneq ($(LTO),)
 android_CFLAGS += -flto

depends/hosts/darwin.mk

@@ -110,7 +110,7 @@ darwin_CXX=env -u C_INCLUDE_PATH -u CPLUS_INCLUDE_PATH \
                -Xclang -internal-externc-isystem$(OSX_SDK)/usr/include
 
 darwin_CFLAGS=-pipe -std=$(C_STANDARD)
-darwin_CXXFLAGS=-pipe
+darwin_CXXFLAGS=-pipe -std=$(CXX_STANDARD)
 
 ifneq ($(LTO),)
 darwin_CFLAGS += -flto

depends/hosts/freebsd.mk

@@ -1,5 +1,5 @@
 freebsd_CFLAGS=-pipe -std=$(C_STANDARD)
-freebsd_CXXFLAGS=-pipe
+freebsd_CXXFLAGS=-pipe -std=$(CXX_STANDARD)
 
 ifneq ($(LTO),)
 freebsd_CFLAGS += -flto

depends/hosts/linux.mk

@@ -1,5 +1,5 @@
 linux_CFLAGS=-pipe -std=$(C_STANDARD)
-linux_CXXFLAGS=-pipe
+linux_CXXFLAGS=-pipe -std=$(CXX_STANDARD)
 
 ifneq ($(LTO),)
 linux_CFLAGS += -flto

depends/hosts/mingw32.mk

@@ -3,7 +3,7 @@ mingw32_CXX := $(host)-g++-posix
 endif
 
 mingw32_CFLAGS=-pipe -std=$(C_STANDARD)
-mingw32_CXXFLAGS=-pipe
+mingw32_CXXFLAGS=-pipe -std=$(CXX_STANDARD)
 
 ifneq ($(LTO),)
 mingw32_CFLAGS += -flto

depends/hosts/netbsd.mk

@@ -1,5 +1,5 @@
 netbsd_CFLAGS=-pipe -std=$(C_STANDARD)
-netbsd_CXXFLAGS=-pipe
+netbsd_CXXFLAGS=-pipe -std=$(CXX_STANDARD)
 
 ifneq ($(LTO),)
 netbsd_CFLAGS += -flto

depends/hosts/openbsd.mk

@@ -1,5 +1,5 @@
 openbsd_CFLAGS=-pipe -std=$(C_STANDARD)
-openbsd_CXXFLAGS=-pipe
+openbsd_CXXFLAGS=-pipe -std=$(CXX_STANDARD)
 
 ifneq ($(LTO),)
 openbsd_CFLAGS += -flto

depends/packages/bdb.mk

@@ -15,7 +15,6 @@ $(package)_config_opts_netbsd=--with-pic
 $(package)_config_opts_openbsd=--with-pic
 $(package)_config_opts_android=--with-pic
 $(package)_cflags+=-Wno-error=implicit-function-declaration
-$(package)_cxxflags+=-std=c++17
 $(package)_cppflags_mingw32=-DUNICODE -D_UNICODE
 endef
 

depends/packages/zeromq.mk

@@ -16,7 +16,6 @@ define $(package)_set_vars
   $(package)_config_opts_netbsd=--with-pic
   $(package)_config_opts_openbsd=--with-pic
   $(package)_config_opts_android=--with-pic
-  $(package)_cxxflags+=-std=c++17
 endef
 
 define $(package)_preprocess_cmds