binman: Get futility by building it

A binary download is not great, since it depends on libraries being
present in the system. Build futility from source instead.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/bintool.py b/tools/binman/bintool.py
index 032179a..a582d9d 100644
--- a/tools/binman/bintool.py
+++ b/tools/binman/bintool.py
@@ -319,7 +319,7 @@
             return result.stdout
 
     @classmethod
-    def build_from_git(cls, git_repo, make_target, bintool_path):
+    def build_from_git(cls, git_repo, make_target, bintool_path, flags=None):
         """Build a bintool from a git repo
 
         This clones the repo in a temporary directory, builds it with 'make',
@@ -330,6 +330,7 @@
             make_target (str): Target to pass to 'make' to build the tool
             bintool_path (str): Relative path of the tool in the repo, after
                 build is complete
+            flags (list of str): Flags or variables to pass to make, or None
 
         Returns:
             tuple:
@@ -341,8 +342,11 @@
         print(f"- clone git repo '{git_repo}' to '{tmpdir}'")
         tools.run('git', 'clone', '--depth', '1', git_repo, tmpdir)
         print(f"- build target '{make_target}'")
-        tools.run('make', '-C', tmpdir, '-j', f'{multiprocessing.cpu_count()}',
-                  make_target)
+        cmd = ['make', '-C', tmpdir, '-j', f'{multiprocessing.cpu_count()}',
+               make_target]
+        if flags:
+            cmd += flags
+        tools.run(*cmd)
         fname = os.path.join(tmpdir, bintool_path)
         if not os.path.exists(fname):
             print(f"- File '{fname}' was not produced")