Update comment to more succint that 8/16-bit composites can't be dire…

…ctly constructed

Earlier the comment looked misleading that composites of 8/16-bit types can't be constructed at all.
As per the GL_EXT_shader_16bit_storage extension, they can't be constructed directly, however, can be constructed indirectly.

glslang/MachineIndependent/ParseHelper.cpp

@@ -8539,7 +8539,7 @@ TIntermTyped* TParseContext::constructBuiltIn(const TType& type, TOperator op, T
  case EOpConstructF16Mat4x4:
  case EOpConstructFloat16:
  basicOp = EOpConstructFloat16;
- // 8/16-bit storage extensions don't support constructing composites of 8/16-bit types,
+ // 8/16-bit storage extensions don't support direct constructing composites of 8/16-bit types,
  // so construct a 32-bit type and convert
  // and do not generate any conversion if it is an identity conversion, i.e. float16_t(<float16_t> var)
  if (!intermediate.getArithemeticFloat16Enabled() && (node->getBasicType() != EbtFloat16)) {
@@ -8563,7 +8563,7 @@ TIntermTyped* TParseContext::constructBuiltIn(const TType& type, TOperator op, T
  case EOpConstructI8Vec4:
  case EOpConstructInt8:
  basicOp = EOpConstructInt8;
- // 8/16-bit storage extensions don't support constructing composites of 8/16-bit types,
+ // 8/16-bit storage extensions don't support direct constructing composites of 8/16-bit types,
  // so construct a 32-bit type and convert
  // and do not generate any conversion if it is an identity conversion, i.e. int8_t(<int8_t> var)
  if (!intermediate.getArithemeticInt8Enabled() && (node->getBasicType() != EbtInt8)) {
@@ -8587,7 +8587,7 @@ TIntermTyped* TParseContext::constructBuiltIn(const TType& type, TOperator op, T
  case EOpConstructU8Vec4:
  case EOpConstructUint8:
  basicOp = EOpConstructUint8;
- // 8/16-bit storage extensions don't support constructing composites of 8/16-bit types,
+ // 8/16-bit storage extensions don't support direct constructing composites of 8/16-bit types,
  // so construct a 32-bit type and convert
  // and do not generate any conversion if it is an identity conversion, i.e. uint8_t(<uint8_t> var)
  if (!intermediate.getArithemeticInt8Enabled() && (node->getBasicType() != EbtUint8)) {
@@ -8611,7 +8611,7 @@ TIntermTyped* TParseContext::constructBuiltIn(const TType& type, TOperator op, T
  case EOpConstructI16Vec4:
  case EOpConstructInt16:
  basicOp = EOpConstructInt16;
- // 8/16-bit storage extensions don't support constructing composites of 8/16-bit types,
+ // 8/16-bit storage extensions don't support direct constructing composites of 8/16-bit types,
  // so construct a 32-bit type and convert
  // and do not generate any conversion if it is an identity conversion, i.e. int16_t(<int16_t> var)
  if (!intermediate.getArithemeticInt16Enabled() && (node->getBasicType() != EbtInt16)) {
@@ -8635,7 +8635,7 @@ TIntermTyped* TParseContext::constructBuiltIn(const TType& type, TOperator op, T
  case EOpConstructU16Vec4:
  case EOpConstructUint16:
  basicOp = EOpConstructUint16;
- // 8/16-bit storage extensions don't support constructing composites of 8/16-bit types,
+ // 8/16-bit storage extensions don't support direct constructing composites of 8/16-bit types,
  // so construct a 32-bit type and convert
  // and do not generate any conversion if it is an identity conversion, i.e. uint16_t(<uint16_t> var)
  if (!intermediate.getArithemeticInt16Enabled() && (node->getBasicType() != EbtUint16)) {