[llvm-strings] Add support for the -a/--all options

[mstorsjo]

Summary

They don't actually change nay behaviour, as llvm-strings currently checks the whole object without looking at individual sections anyway.

This allows using llvm-strings in a context that explicitly passes the -a option.

[dberris]

LGTM

test/tools/llvm-strings/all-sections.test

+RUN: llvm-strings -a %S/Inputs/abcd | FileCheck %s
+RUN: llvm-strings --all %S/Inputs/abcd | FileCheck %s
+CHECK: abcd

tools/llvm-strings/llvm-strings.cpp

 static cl::alias PrintFileNameShort("f", cl::desc(""),
                                     cl::aliasopt(PrintFileName));
 
 static cl::opt<int>
     MinLength("bytes", cl::desc("Print sequences of the specified length"),
               cl::init(4));
 static cl::alias MinLengthShort("n", cl::desc(""), cl::aliasopt(MinLength));
 
+static cl::opt<bool>
+    AllSections("all",
+                  cl::desc("Check all sections, not just the data section"));
+static cl::alias AllSectionsShort("a", cl::desc(""),
+                                    cl::aliasopt(AllSections));
+
 enum radix { none, octal, hexadecimal, decimal };
 static cl::opt<radix>
     Radix("radix", cl::desc("print the offset within the file"),
           cl::values(clEnumValN(octal, "o", "octal"),
                      clEnumValN(hexadecimal, "x", "hexadecimal"),
                      clEnumValN(decimal, "d", "decimal")),
           cl::init(none));
 static cl::alias RadixShort("t", cl::desc(""), cl::aliasopt(Radix));