Pseudoinstructions sgt and sgtu not recognised

[fer-amdias]

When running a piece of code such as:

li t0, 1
li t1, 2
sgt t0, t1, t0

RARS will run it just fine, yet FPGRARS will complain:

[error]: Unknown instruction 'sgt'
   --> test.asm at line 3, column 2
 2  | li t1, 2
 3  | sgt t0, t1, t
......^ Here

The same will happen for its unsigned counterpart, sgtu.

li t0, 1
li t1, 2
sgtu t0, t1, t0

   [error]: Unknown instruction 'sgtu'
   --> fpgrars_test.asm at line 3, column 2
 2  | li t1, 2
 3  | sgtu t0, t1, t
......^ Here

Strangely, this does not happen with stgz. The code runs just fine.

li t1, 2
sgtz t0, t1

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