Modify the CI script to fall back to nmake if jom is missing

Fixes #3629

src/scripts/ci_build.py

@@ -522,6 +522,20 @@ def have_prog(prog):
                 return True
     return False
 
+def validate_make_tool(make_tool):
+    if make_tool == '':
+        return 'make'
+
+    if make_tool not in ['nmake', 'jom', 'make']:
+        raise Exception("Don't know about %s as a make tool" % (make_tool))
+
+    # Hack to work around jom occasionally fail to install
+    # https://github.com/randombit/botan/issues/3629
+    if make_tool == 'jom' and not have_prog('jom'):
+        return 'nmake'
+
+    return make_tool
+
 def main(args=None):
     """
     Parse options, do the things
@@ -635,13 +649,10 @@ def main(args=None):
 
         cmds.append([py_interp, os.path.join(root_dir, 'configure.py')] + config_flags)
 
-        if options.make_tool == '':
-            options.make_tool = 'make'
-
-        make_cmd = [options.make_tool]
+        make_cmd = [validate_make_tool(options.make_tool)]
         if build_dir != '.':
             make_cmd = ['indir:%s' % build_dir] + make_cmd
-        if options.build_jobs > 1 and options.make_tool != 'nmake':
+        if options.build_jobs > 1 and make_tool != 'nmake':
             make_cmd += ['-j%d' % (options.build_jobs)]
 
         make_cmd += ['-k']