Resolve complation issues with -fno-common (default from gcc-10)

Extends the MakeHeader script to auto-generate correct "extern"
function declarations in some cases that it currently does not.

Related to https://github.com/hishamhm/htop/pull/981

scripts/MakeHeader.py

@@ -54,8 +54,10 @@ for line in file.readlines():
          elif line.startswith("typedef struct"):
             state = SKIP
          elif line[-1] == "{":
-            out.write( line[:-2].replace("inline", "extern") + ";\n" )
+            out.write("extern " + line[:-2].replace("inline ", "") + ";\n")
             state = SKIP
+         elif line[-1] == ";":
+            out.write("extern " + line + "\n")
          else:
             out.write( line + "\n")
          is_blank = False