Merge remote-tracking branch 'tor-gitlab/mr/355' into maint-0.4.5

diff --cc configure.ac
index dfd7a495bbaa25d84e511809f8871cd4db856c95,179e8915b12f629c61c54a7d2d572804b0725d9e..a85d530bed1cbe128221d34c3a3e7f92a7f3e5bb
--- 1/configure.ac
--- 2/configure.ac
+++ b/configure.ac
@@@ -437,27 -290,23 +437,31 @@@ AC_PATH_PROG([ASCIIDOC], [asciidoc], no
  AC_PATH_PROGS([A2X], [a2x a2x.py], none)
  
  AM_CONDITIONAL(USE_ASCIIDOC, test "x$asciidoc" = "xtrue")
 +AM_CONDITIONAL(BUILD_MANPAGE, [test "x$enable_manpage" != "xno"])
 +AM_CONDITIONAL(BUILD_HTML_DOCS, [test "x$enable_html_manual" != "xno"])
  
  AM_PROG_CC_C_O
- AC_PROG_CC_C99
+ 
+ dnl Before autoconf 2.70, AC_PROG_CC_C99 is supposedly necessary for some
+ dnl compilers if you wan't C99 support. Starting with 2.70, it is obsolete and
+ dnl forbidden.
+ m4_version_prereq([2.70], [:], [AC_PROG_CC_C99])
  
 -AC_ARG_VAR([PYTHON], [path to Python binary])
 -AC_CHECK_PROGS(PYTHON, [ \
 +AC_CACHE_CHECK([for Python 3], [tor_cv_PYTHON],
 +   [AC_PATH_PROGS_FEATURE_CHECK([PYTHON], [ \
        python3 \
        python3.8 python3.7 python3.6 python3.5 python3.4 \
 -      python \
 -      python2 python2.7])
 +      python ],
 +   [["$ac_path_PYTHON" -c 'import sys; sys.exit(sys.version_info[0]<3)' && tor_cv_PYTHON="$ac_path_PYTHON" ac_path_PYTHON_found=:]] )])
 +AC_SUBST([PYTHON], [$tor_cv_PYTHON])
 +
 +PYTHON="$tor_cv_PYTHON"
 +
  if test "x$PYTHON" = "x"; then
 -  AC_MSG_WARN([Python unavailable; some tests will not be run.])
 +  tor_incr_n_warnings
 +  AC_MSG_WARN([Python 3 unavailable; some tests will not be run.])
  fi
 +
  AM_CONDITIONAL(USEPYTHON, [test "x$PYTHON" != "x"])
  
  dnl List all external rust crates we depend on here. Include the version