build: allow Python 3.8

PR-URL: #30194
Reviewed-By: Christian Clauss <cclauss@me.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>

BUILDING.md

@@ -246,7 +246,7 @@ transition before the year-end deadline.
 * GNU Make 3.81 or newer
 * Python (see note above)
   * Python 2.7
-  * Python 3.5, 3.6, and 3.7 are experimental.
+  * Python 3.5, 3.6, 3.7, and 3.8 are experimental.
 
 Installation via Linux package manager can be achieved with:
 
@@ -262,7 +262,7 @@ FreeBSD and OpenBSD users may also need to install `libexecinfo`.
 * Xcode Command Line Tools >= 10 for macOS
 * Python (see note above)
   * Python 2.7
-  * Python 3.5, 3.6, and 3.7 are experimental.
+  * Python 3.5, 3.6, 3.7, and 3.8 are experimental.
 
 macOS users can install the `Xcode Command Line Tools` by running
 `xcode-select --install`. Alternatively, if you already have the full Xcode

configure

@@ -7,6 +7,7 @@
 # pyenv will alert which shims are available and then will fail the build.
 _=[ 'exec' '/bin/sh' '-c' '''
 test ${TRAVIS} && exec python "$0" "$@"  # workaround for pyenv on Travis CI
+which python3.8 >/dev/null && exec python3.8 "$0" "$@"
 which python3.7 >/dev/null && exec python3.7 "$0" "$@"
 which python3.6 >/dev/null && exec python3.6 "$0" "$@"
 which python3.5 >/dev/null && exec python3.5 "$0" "$@"
@@ -20,7 +21,7 @@ import sys
 from distutils.spawn import find_executable
 
 print('Node configure: Found Python {0}.{1}.{2}...'.format(*sys.version_info))
-acceptable_pythons = ((2, 7), (3, 7), (3, 6), (3, 5))
+acceptable_pythons = ((3, 8), (3, 7), (3, 6), (3, 5), (2, 7))
 if sys.version_info[:2] in acceptable_pythons:
   import configure
 else: