convert to uint8_t* for binary data to fix -Wnarrowing build errors

Newer gcc versions default to -Werror=narrowing when using newer C++
standards (which we do).  This causes issues when we try to stuff a
value like 0xea into a char -- the value is out of range for signed
char bytes.  That's when gcc throws an error:
.../bytereader_unittest.cc: In member function 'virtual void Reader_DW_EH_PE_absptr4_Test::TestBody()':
.../bytereader_unittest.cc:400:55: error: narrowing conversion of '234' from 'int' to 'char' inside { } [-Wnarrowing]

BUG=chromium:579384
TEST=`make check` passes
R=mark@chromium.org

Review URL: https://codereview.chromium.org/1605153004 .

src/common/dwarf/dwarf2diehandler.cc

@@ -32,6 +32,7 @@
 // See dwarf2diehandler.h for details.
 
 #include <assert.h>
+#include <stdint.h>
 
 #include <string>
 
@@ -167,7 +168,7 @@ void DIEDispatcher::ProcessAttributeReference(uint64 offset,
 void DIEDispatcher::ProcessAttributeBuffer(uint64 offset,
                                            enum DwarfAttribute attr,
                                            enum DwarfForm form,
-                                           const char* data,
+                                           const uint8_t *data,
                                            uint64 len) {
   HandlerStack &current = die_handlers_.top();
   // This had better be an attribute of the DIE we were meant to handle.