Issue warning or error if generated transformation cannot be applied

[clementval]

<!-- CLAW default configuration. This file should not be edited ! -->
<claw version="0.3">
  <!-- Transformation parameters -->
  <global>
    <!-- Default general values -->
    <parameter key="default_target" value="gpu"/>
    <parameter key="default_directive" value="openacc"/>

    <!-- OpenACC default information -->
    <!-- Define the default values to be used for the clauses. If value set to 0, compiler default value used. -->
    <parameter key="openacc_vector_length" value="128"/> <!-- vector_length(128) -->
    <parameter key="openacc_num_gangs" value="8"/>       <!-- num_gangs(8) -->
    <parameter key="openacc_num_workers" value="8"/>     <!-- num_workers(8) -->
    <!-- Specify the order of generation of clauses when nested loops are generated -->
    <!-- possible values are vector_gang, gang_vector, vector, gang, none -->
    <parameter key="openacc_execution_mode" value="vector_gang"/>
  </global>
  <!-- Transformation groups -->
  <groups>
    <!-- Low-level transformations -->
    <group type="independent" name="internal-xcodeml"    class="cx2x.translator.transformation.utility.XcodeMLWorkaround" />
    <group type="independent" name="remove"              class="cx2x.translator.transformation.utility.UtilityRemove" />
    <group type="independent" name="primitive"           class="cx2x.translator.transformation.openacc.DirectivePrimitive" />
    <group type="independent" name="array-transform"     class="cx2x.translator.transformation.loop.ArrayTransform" />
    <group type="independent" name="loop-extract"        class="cx2x.translator.transformation.loop.LoopExtraction" />
    <group type="dependent"   name="loop-fusion"         class="cx2x.translator.transformation.loop.LoopFusion" />
    <group type="independent" name="loop-hoist"          class="cx2x.translator.transformation.loop.LoopHoist" />
    <group type="independent" name="loop-interchange"    class="cx2x.translator.transformation.loop.LoopInterchange" />
    <group type="independent" name="on-the-fly"          class="cx2x.translator.transformation.claw.ArrayToFctCall" />
    <group type="independent" name="kcache"              class="cx2x.translator.transformation.claw.Kcaching" />
    <group type="independent" name="if-extract"          class="cx2x.translator.transformation.loop.IfExtract" />
    <!-- High-level transformations -->
    <group type="independent" name="parallelize"         class="cx2x.translator.transformation.claw.parallelize.Parallelize" />
    <group type="independent" name="parallelize-forward" class="cx2x.translator.transformation.claw.parallelize.ParallelizeForward" />
  </groups>
</claw>

!$claw loop-fusion
DO i=1,10
END DO

!$claw loop-hoist(i) fusion
IF (.TRUE.) THEN
END IF
DO i=1,10
END DO

With this configuration, the fusion cannot be applied as the fusion transformations are applied before the hoisting transformations