debian: Don't install gcc g++ on debian.

gmake assumes default CC is cc, CXX is g++ (not c++).
In order to make this sane (c++), we check if the shell variable CXX was set
and if so we honor it, else we set CXX to c++.

GNUmakefile

@@ -5,6 +5,14 @@ ifdef CONFIG
 	DEBUG ?= 0
 	REPRODUCIBLE ?= 0
 
+	# gmake's default CXX is g++, we prefer c++
+	SHELL_CXX = $(shell printenv CXX)
+	ifeq ($(SHELL_CXX),)
+		CXX=c++
+	else
+		CXX=$(SHELL_CXX)
+	endif
+
 	include $(CONFIG)
 
 	CFLAGS = -Wall \

build.sh

@@ -686,7 +686,7 @@ make_boot_image() {
 }
 
 install_deps_apt() {
-    sudo apt install --yes libc6-dev libpango1.0-dev libx11-dev xorg-dev libgtk2.0-dev gtk2-engines-pixbuf libgtkglext1-dev wget git git-doc rlwrap clang gcc make screen tmux libssl-dev g++
+    sudo apt install --yes libc6-dev libpango1.0-dev libx11-dev xorg-dev libgtk2.0-dev gtk2-engines-pixbuf libgtkglext1-dev wget git git-doc rlwrap clang make screen tmux libssl-dev
     check_ret sudo
 }
 

vm/Config.linux

@@ -5,6 +5,9 @@ LIBS = -ldl -lm -lrt -lpthread -Wl,--export-dynamic
 
 # clang spams warnings if we use -Wl,--no-as-needed with -c
 # -Wl,--no-as-needed is a gcc optimization, not required
-ifneq ($(CXX),clang++)
+# we want to work with g++ aliased as c++ here, too
+IS_GCC = $(shell $(CXX) --version | grep '(GCC)')
+
+ifdef ($(IS_GCC))
 	SITE_CFLAGS += -Wl,--no-as-needed
 endif