Disallow multiple function prototypes in ESSL 1.00 The same function can't be declared twice in ESSL 1.00. In ESSL 3.00 this is allowed. A function prototype following the definition of that function is not interpreted as redeclaration, and the shader compiler continues to allow this. BUG=angleproject:1067 TEST=angle_unittests, dEQP-GLES2.functional.shaders.functions.invalid.double_declare* Change-Id: I6d2ddafd456d378d92839600f19069ad1cd19aff Reviewed-on: https://chromium-review.googlesource.com/320082 Tryjob-Request: Olli Etuaho <oetuaho@nvidia.com> Tested-by: Olli Etuaho <oetuaho@nvidia.com> Reviewed-by: Jamie Madill <jmadill@chromium.org>