waf: add option --enable-benchmarks

In the future, gbenchmark will be build using a cmake waf tool, which will
require cmake to be installed. We add this option so that users without cmake
can continue use the build system with no problems.

README-WAF.md

@@ -69,7 +69,7 @@ The programs in ardupilot are categorized into the following groups:
  - tools
  - examples: *programs that show how certain libraries are used or to simply
    test their operation*
- - benchmarks
+ - benchmarks: *requires `--enable-benchmarks` during configurarion*
  - tests: *basically unit tests to ensure changes don't break the system's
    logic*
 

wscript

@@ -64,6 +64,11 @@ def options(opt):
                  help='Don\'t update git submodules. Useful for building ' +
                       'with submodules at specific revisions.')
 
+    g.add_option('--enable-benchmarks',
+                 action='store_true',
+                 default=False,
+                 help='Enable benchmarks')
+
 def configure(cfg):
     cfg.env.BOARD = cfg.options.board
     # use a different variant for each board
@@ -79,7 +84,8 @@ def configure(cfg):
     cfg.load('waf_unit_test')
     cfg.load('mavgen')
     cfg.load('git_submodule')
-    cfg.load('gbenchmark')
+    if cfg.options.enable_benchmarks:
+        cfg.load('gbenchmark')
     cfg.load('gtest')
     cfg.load('static_linking')