glsl: Merge "candidates are: " message to the previous line.

glsl: Merge "candidates are: " message to the previous line.

Previously, when we hit a "no matching function" error, it looked like:

0:0(0): error: no matching function for call to `cos()'
0:0(0): error: candidates are: float cos(float)
0:0(0): error:                vec2 cos(vec2)
0:0(0): error:                vec3 cos(vec3)
0:0(0): error:                vec4 cos(vec4)

Now it looks like:

0:0(0): error: no matching function for call to `cos()'; candidates are:
0:0(0): error:    float cos(float)
0:0(0): error:    vec2 cos(vec2)
0:0(0): error:    vec3 cos(vec3)
0:0(0): error:    vec4 cos(vec4)

This is not really any worse and removes the need for the prefix variable.
It will also help with the next commit's refactoring.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Chris Forbes <chrisf@ijw.co.nz>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>