fix: register gcc-11/g++-11 as the generic gcc/g++/cc/c++ alternatives

Installing gcc-11 and g++-11 only provides the versioned binaries; no
generic gcc/g++/cc/c++ command existed, so node-gyp (and any other
tool invoking the plain compiler names, as make-based builds do)
failed with "g++: No such file or directory" even after make was
installed.

Author: Mearman

Dockerfile

@@ -13,6 +13,10 @@ ENV DEBIAN_FRONTEND=noninteractive
 RUN apt-get update \
     && apt-get install -y --no-install-recommends \
         gcc-11 g++-11 make unzip \
+    && update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-11 100 \
+    && update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-11 100 \
+    && update-alternatives --install /usr/bin/cc cc /usr/bin/gcc-11 100 \
+    && update-alternatives --install /usr/bin/c++ c++ /usr/bin/g++-11 100 \
     && rm -rf /var/lib/apt/lists/*
 
 # Bun (JS runtime), installed system-wide. Explicit bash -c (the default RUN