glcpp: Resolve implicit GLSL version to 100 if the API is ES.

glcpp: Resolve implicit GLSL version to 100 if the API is ES.

Fixes a regression since b2d1c579 where ES shaders without a #version
declaration would fail to compile if their precision declaration was
wrapped in the standard #ifdef GL_ES check.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=74066
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>