Limit size of large files test for VxWorks

VxWorks doesn't allow mapping file beyond EOF, adjust tests to encompass
that.

Additionally, for testing on VxWorks we use use builtin /tmp which is a
RAM disk (in case of VxWorks-supported imx.6 bord which have 1GB of
RAM), set max size of tested large file to 256MB, 28 bits.

Task-number: QTBUG-115777
Change-Id: I73cbe112331b7cb95d80bb44b792578a1eb88a07
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit 7678edebba7e93ce648714cd6849023e2880813f)

tests/auto/corelib/io/largefile/tst_largefile.cpp

@@ -46,6 +46,10 @@ public:
         // This means that files are limited to 2 GB − 1 bytes.
         // Limit max size to 256MB
         maxSizeBits = 28; // 256 MiB
+    #elif defined(Q_OS_VXWORKS)
+        // VxWorks doesn't support sparse files, also, default /tmp directory is a RAM-disk which
+        // limits its capacity.
+        maxSizeBits = 28; // 256 MiB
     #elif defined(QT_LARGEFILE_SUPPORT)
         maxSizeBits = 36; // 64 GiB
     #else
@@ -491,12 +495,16 @@ void tst_LargeFile::mapFile()
 //Linux: memory-mapping beyond EOF usually succeeds, but depends on the filesystem
 //  32-bit: limited to 44-bit offsets (when sizeof(off_t) == 8)
 //Windows: memory-mapping beyond EOF is not allowed
+//VxWorks: memory-mapping beyond EOF is not allowed
 void tst_LargeFile::mapOffsetOverflow()
 {
     enum {
 #ifdef Q_OS_WIN
         Succeeds = false,
         MaxOffset = 63
+#elif defined(Q_OS_VXWORKS)
+        Succeeds = false,
+        MaxOffset = 8 * sizeof(QT_OFF_T) - 1
 #else
         Succeeds = true,
 #  if (defined(Q_OS_LINUX) || defined(Q_OS_ANDROID)) && Q_PROCESSOR_WORDSIZE == 4