libvmdump: Increase message buffer size

The message buffer of DumpException doesn't account for additional
strings such as strerror(), device nodes, or filenames. Make it a bit
larger to be safe.

This fixes the following GCC8 compile warnings:

In file included from vm_dump.h:62,
                 from vm_dump.cpp:17:
dump.h: In static member function ‘static Dump::DumpType
VMDump::getDumpType(const char*)’:
dump.h:46:16: warning: ‘ (’ directive writing 2 bytes into a region of size
between 1 and 200 [-W format-overflow=]
   sprintf(msg, "%s (%s)", m, strerror(errno));
                ^~~~~~~~~
dump.h:46:10: note: ‘sprintf’ output 4 or more bytes (assuming 203) into a
destination of size 200
   sprintf(msg, "%s (%s)", m, strerror(errno));
   ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
dump.h:46:16: warning: ‘ (’ directive writing 2 bytes into a region of size
between 1 and 200 [-W format-overflow=]
   sprintf(msg, "%s (%s)", m, strerror(errno));
                ^~~~~~~~~
dump.h:46:10: note: ‘sprintf’ output 4 or more bytes (assuming 203) into a
destination of size 200
   sprintf(msg, "%s (%s)", m, strerror(errno));
   ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
dump.h:46:16: warning: ‘ (’ directive writing 2 bytes into a region of size
between 1 and 200 [-W format-overflow=]
   sprintf(msg, "%s (%s)", m, strerror(errno));
                ^~~~~~~~~
dump.h:46:10: note: ‘sprintf’ output 4 or more bytes (assuming 203) into a
destination of size 200
   sprintf(msg, "%s (%s)", m, strerror(errno));
   ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

libvmdump/dump.h

@@ -35,7 +35,7 @@ public:
 	const char *what(void) const { return msg; }
 	int code(void) const { return errorCode; }
 protected:
-	char msg[200];
+	char msg[2048];
 	int  errorCode;
 };