feat: Check whether GCC is installed in initenv.sh

- Before proceeding with installation of Python dependencies, check
  whether the 'gcc' command is available by running it with the
  --version argument.  If it is not available, print a helpful message
  and exit.
- For the current set of Python dependencies, without GCC, the build
  process fails when building the crypt-r package.  According to the
  error message, on my system the exact command it tries to run is
  'x86_64-linux-gnu-gcc', but rather than depend on this variant
  specifically, the script checks for the generic 'gcc' command, so as
  to avoid coupling the check to an architecture or operating system.
  Similar problems arise if we attempt to check for packages by name;
  the compiler binary is provided by 'gcc-11', but the symlinks that
  provide the unversioned commands (as used by the Python build) come
  from a package named 'gcc'.  Trying to be too precise in what we
  check for could lead to unnecessary failures in some environments,
  or become a maintenance challenge in the future.  For that reason,
  this change simply attempts to run 'gcc' and uses that as a
  probably-sufficient proxy for having what the Python package install
  will need.

scripts/initenv.sh

@@ -9,9 +9,9 @@ if command -v lsb_release 2>&1 >/dev/null; then
         echo "You need to install python3-dev for installing the other dependencies."
         exit 1
       fi
-      if ! dpkg -l | grep build-essential 2>&1 >/dev/null
+      if ! gcc --version 2>&1 >/dev/null
       then
-        echo "You need to install build-essential for building Python dependencies."
+        echo "You need to install gcc for building Python dependencies."
         exit 1
       fi
       ;;