Fix alignment for strings on platforms where alignment matters (#13)

Previously, LttngHelpers.h would pass down an alignment characterisc of the input data, rather than the eventual UTF8 output.

Fix this by targeting the required alignment of either the UTF8 string or the uint16_t that will prepend sequences.

include/lttngh/LttngHelpers.h

@@ -464,7 +464,7 @@ lttngh_DataDescCreateStringUtf16(const char16_t *str) {
   }
   struct lttngh_DataDesc dd = {
       str, (unsigned)(strEnd - str) * (unsigned)sizeof(char16_t),
-      lttng_alignof(char16_t), lttngh_DataType_StringUtf16Transcoded, 0};
+      lttng_alignof(char), lttngh_DataType_StringUtf16Transcoded, 0};
   return dd;
 }
 
@@ -480,7 +480,7 @@ static inline struct lttngh_DataDesc lttngh_DataDescCreateSequenceUtf16(
 static inline struct lttngh_DataDesc
 lttngh_DataDescCreateSequenceUtf16(const char16_t *str, uint16_t length) {
   struct lttngh_DataDesc dd = {str, length * (unsigned)sizeof(char16_t),
-                               lttng_alignof(char16_t),
+                               lttng_alignof(uint16_t),
                                lttngh_DataType_SequenceUtf16Transcoded, 0};
   return dd;
 }
@@ -499,7 +499,7 @@ lttngh_DataDescCreateStringUtf32(const char32_t *str) {
   }
   struct lttngh_DataDesc dd = {
       str, (unsigned)(strEnd - str) * (unsigned)sizeof(char32_t),
-      lttng_alignof(char32_t), lttngh_DataType_StringUtf32Transcoded, 0};
+      lttng_alignof(char), lttngh_DataType_StringUtf32Transcoded, 0};
   return dd;
 }
 
@@ -515,7 +515,7 @@ static inline struct lttngh_DataDesc lttngh_DataDescCreateSequenceUtf32(
 static inline struct lttngh_DataDesc
 lttngh_DataDescCreateSequenceUtf32(const char32_t *str, uint16_t length) {
   struct lttngh_DataDesc dd = {str, length * (unsigned)sizeof(char32_t),
-                               lttng_alignof(char32_t),
+                               lttng_alignof(uint16_t),
                                lttngh_DataType_SequenceUtf32Transcoded, 0};
   return dd;
 }