Fix compilation with strict format checking

abs() is bit tricky in C++ and this use of abs is returning double.
FXSYS_snprintf is strictly checking this on Fedora 24 and
results in:
../../third_party/pdfium/fpdfsdk/fsdk_baseannot.cpp:309:18: error:
 format specifies type 'int' but the argument has type
 'typename __gnu_cxx::__enable_if<__is_integer<signed char>::__value, double>::__type'
 (aka 'double') [-Werror,-Wformat]

Review-Url: https://codereview.chromium.org/2124083002
diff --git a/fpdfsdk/fsdk_baseannot.cpp b/fpdfsdk/fsdk_baseannot.cpp
index 9b21473..2ef2871 100644
--- a/fpdfsdk/fsdk_baseannot.cpp
+++ b/fpdfsdk/fsdk_baseannot.cpp
@@ -289,7 +289,7 @@
   else
     str1 += "+";
   CFX_ByteString str2;
-  str2.Format("%02d:%02u", abs(dt.tzHour), dt.tzMinute);
+  str2.Format("%02d:%02u", std::abs(static_cast<int>(dt.tzHour)), dt.tzMinute);
   return str1 + str2;
 }
 
@@ -305,8 +305,8 @@
   else
     dtStr += CFX_ByteString("+");
   memset(tempStr, 0, sizeof(tempStr));
-  FXSYS_snprintf(tempStr, sizeof(tempStr) - 1, "%02d'%02u'", abs(dt.tzHour),
-                 dt.tzMinute);
+  FXSYS_snprintf(tempStr, sizeof(tempStr) - 1, "%02d'%02u'",
+                 std::abs(static_cast<int>(dt.tzHour)), dt.tzMinute);
   dtStr += CFX_ByteString(tempStr);
   return dtStr;
 }