message: add DUCKDB_SOURCE_ID definition to amalgamation.py
  The DUCKDB_SOURCE_ID definition isn't defined from the CMakeLists like
  when doing a `make debug` so I added a equivalent function to
  amalgamation.py to define the DUCKDB_SOURCE_ID in the amalgamated file.
diff: @@ -3,6 +3,7 @@ import os
  import re
  import sys
  import shutil
  +import subprocess
  amal_dir = os.path.join('src', 'amalgamation')
  header_file = os.path.join(amal_dir, "duckdb.hpp")
  source_file = os.path.join(amal_dir, "duckdb.cpp")
  @@ -143,6 +144,9 @@ def copy_if_different(src, dest):
  print("Copying " + src + " to " + dest)
  shutil.copyfile(src, dest)
  +def git_commit_hash():
  + return subprocess.check_output(['git','log','-1','--format=%h']).strip()
  +
  def generate_amalgamation(source_file, header_file):
  # now construct duckdb.hpp from these headers
  print("-----------------------")
  @@ -152,6 +156,7 @@ def generate_amalgamation(source_file, header_file):
  hfile.write("// See https://raw.githubusercontent.com/cwida/duckdb/master/LICENSE for licensing information\n\n")
  hfile.write("#pragma once\n")
  hfile.write("#define DUCKDB_AMALGAMATION 1\n")
  + hfile.write("#define DUCKDB_SOURCE_ID \"%s\"\n" % git_commit_hash())
  for fpath in main_header_files:
  hfile.write(write_file(fpath))
  