Squash GCC 4.8 fixes

gldual: Fix build with gcc 4.8+
Use -Wno-error=unused-parameter with gcc >= 4.8

gl2_jni: Fix build with gcc 4.8+
Use -Wno-error=unused-parameter with gcc >= 4.8

gl_perfapp: Fix build with gcc 4.8+
Use -Wno-error=unused-parameter with gcc >= 4.8

gl_jni: Fix build with gcc 4.8+
Use -Wno-error=unused-parameter with gcc >= 4.8