Enable JIT, install g++

Erlang 24 provide JIT support that requires c++17-compatible compiler.
Without the g++ package, `autoconf` considers this support missing and
therefore silently disables JIT. This commits makes sure that:
1. g++ is installed (this makes `autoconf` detect it correctly as
   c++17-compatible)
2. Explicitly enables JIT so that it fails in case something changes in
   the future. JIT is a great feature so we don't want it being silently
   turned off for any reason.

Co-authored-by: Michal Kuratczyk <mkuratczyk@vmware.com>

Author: mkuratczyk

3.8-rc/alpine/Dockerfile

@@ -59,6 +59,7 @@ RUN set -eux; \
 		autoconf \
 		dpkg-dev dpkg \
 		gcc \
+		g++ \
 		gnupg \
 		libc-dev \
 		linux-headers \
@@ -138,6 +139,7 @@ RUN set -eux; \
 		--disable-hipe \
 		--disable-sctp \
 		--disable-silent-rules \
+		--enable-jit
 		--enable-clock-gettime \
 		--enable-hybrid-heap \
 		--enable-kernel-poll \

3.8-rc/ubuntu/Dockerfile

@@ -65,6 +65,7 @@ RUN set -eux; \
 		ca-certificates \
 		dpkg-dev \
 		gcc \
+		g++ \
 		gnupg \
 		libncurses5-dev \
 		make \
@@ -145,6 +146,7 @@ RUN set -eux; \
 		--disable-hipe \
 		--disable-sctp \
 		--disable-silent-rules \
+		--enable-jit \
 		--enable-clock-gettime \
 		--enable-hybrid-heap \
 		--enable-kernel-poll \