HLSL: fix several issues in mat construction from scalars

This fixes:

1. A compilation error when assigning scalars to matricies

2. A semantic error in matrix construction from scalars.  This was
initializing the diagonal, where HLSL semantics require the scalar be
replicated to every matrix element.

3. Functions accepting mats can be called with scalars, which will
be shape-converted to the matrix type.  This was previously failing
to match the function signature.

NOTE: this does not yet handle complex scalars (a function call,
say) used to construct matricies.  That'll be added when the
node replicator service is available.  For now, there's an assert.

There's one new test (hlsl.scalar2matrix.frag).  An existing test
lsl.type.half.frag changes, because of (2) above, and a negative
test error message changes due to (3) above.

Fixes #923.

glslang/MachineIndependent/Intermediate.cpp

@@ -1043,6 +1043,32 @@ TIntermTyped* TIntermediate::addShapeConversion(const TType& type, TIntermTyped*
     // The new node that handles the conversion
     TOperator constructorOp = mapTypeToConstructorOp(type);
 
+    // HLSL has custom semantics for scalar->mat shape conversions.
+    if (source == EShSourceHlsl) {
+        if (node->getType().isScalarOrVec1() && type.isMatrix()) {
+
+            // HLSL semantics: the scalar (or vec1) is replicated to every component of the matrix.  Left to its
+            // own devices, the constructor from a scalar would populate the diagonal.  This forces replication
+            // to every matrix element.
+
+            // Note that if the node is complex (e.g, a function call), we don't want to duplicate it here
+            // repeatedly, so we copy it to a temp, then use the temp.
+            const int matSize = type.getMatrixRows() * type.getMatrixCols();
+            TIntermAggregate* rhsAggregate = new TIntermAggregate();
+
+            const bool isSimple = (node->getAsSymbolNode() != nullptr) || (node->getAsConstantUnion() != nullptr);
+
+            if (!isSimple) {
+                assert(0); // TODO: use node replicator service when available.
+            }
+            
+            for (int x=0; x<matSize; ++x)
+                rhsAggregate->getSequence().push_back(node);
+
+            return setAggregateOperator(rhsAggregate, constructorOp, type, node->getLoc());
+        }
+    }
+
     // scalar -> vector or vec1 -> vector or
     // vector -> scalar or
     // bigger vector -> smaller vector