[clang-tidy] Replace deprecated C headers

Deprecated with C++14.

Found with modernize-deprecated-headers
Signed-off-by: Rosen Penev <rosenp@gmail.com>

src/gflags.cc

@@ -90,18 +90,18 @@
 #include "config.h"
 #include "gflags/gflags.h"
 
-#include <assert.h>
-#include <ctype.h>
-#include <errno.h>
+#include <cassert>
+#include <cctype>
+#include <cerrno>
 #if defined(HAVE_FNMATCH_H)
 #  include <fnmatch.h>
 #elif defined(HAVE_SHLWAPI_H)
 #  define NO_SHLWAPI_ISOS
 #  include <shlwapi.h>
 #endif
-#include <stdarg.h> // For va_list and related operations
-#include <stdio.h>
-#include <string.h>
+#include <cstdarg> // For va_list and related operations
+#include <cstdio>
+#include <cstring>
 
 #include <algorithm>
 #include <map>

src/gflags_completions.cc

@@ -46,9 +46,9 @@
 //     5a) Force bash to place most-relevent groups at the top of the list
 //     5b) Trim most flag's descriptions to fit on a single terminal line
 
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>   // for strlen
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>   // for strlen
 
 #include <set>
 #include <string>

src/gflags_reporting.cc

@@ -48,10 +48,10 @@
 // called after all flag-values have been assigned, that is, after
 // parsing the command-line.
 
-#include <stdio.h>
-#include <string.h>
-#include <ctype.h>
-#include <assert.h>
+#include <cstdio>
+#include <cstring>
+#include <cctype>
+#include <cassert>
 #include <string>
 #include <vector>