[llvm-readelf] Make llvm-readelf more compatible with GNU readelf.

Summary:
This change adds a bunch of options that GNU readelf supports. There is one breaking change when invoked as `llvm-readobj`, and three breaking changes when invoked as `llvm-readelf`:
 - Add --all (implies --file-header, --program-headers, etc.)
 - [Breaking] -a is --all instead of --arm-attributes
 - Add --file-header as an alias for --file-headers
 - Replace --sections with --sections-headers, keeping --sections as an alias for it
 - Add --relocs as an alias for --relocations
 - Add --dynamic as an alias for --dynamic-table
 - Add --segments as an alias for --program-headers
 - Add --section-groups as an alias for --elf-section-groups
 - Add --dyn-syms as an alias for --dyn-symbols
 - Add --syms as an alias for --symbols
 - Add --histogram as an alias for --elf-hash-histogram
 - [Breaking] When invoked as `llvm-readelf`, -s is --symbols instead of --sections
 - [Breaking] When invoked as `llvm-readelf`, -t is no longer an alias for --symbols

Reviewers: MaskRay, phosek, mcgrathr, jhenderson

Reviewed By: MaskRay, jhenderson

Subscribers: sbc100, aheejin, edd, jhenderson, silvas, echristo, compnerd, kristina, javed.absar, kristof.beyls, llvm-commits, Bigcheese

Differential Revision: https://reviews.llvm.org/D54124

llvm-svn: 346685
diff --git a/llvm/test/tools/llvm-readobj/symbols.test b/llvm/test/tools/llvm-readobj/symbols.test
index 1a0cacd..e68d654 100644
--- a/llvm/test/tools/llvm-readobj/symbols.test
+++ b/llvm/test/tools/llvm-readobj/symbols.test
@@ -1,10 +1,19 @@
-RUN: llvm-readobj -t %p/Inputs/trivial.obj.coff-i386 \
+RUN: llvm-readobj --symbols %p/Inputs/trivial.obj.coff-i386 \
 RUN:   | FileCheck %s -check-prefix COFF
-RUN: llvm-readobj -t %p/Inputs/trivial.obj.elf-i386 \
+RUN: llvm-readobj --symbols %p/Inputs/trivial.obj.elf-i386 \
 RUN:   | FileCheck %s -check-prefix ELF
-RUN: llvm-readobj -t %p/Inputs/trivial.obj.wasm \
+RUN: llvm-readobj --symbols %p/Inputs/trivial.obj.wasm \
 RUN:   | FileCheck %s -check-prefix WASM
 
+# Check flag aliases produce identical output.
+RUN: llvm-readobj --symbols %p/Inputs/trivial.obj.elf-i386 > %t.symbols
+RUN: llvm-readobj --syms %p/Inputs/trivial.obj.elf-i386 > %t.syms
+RUN: cmp %t.symbols %t.syms
+RUN: llvm-readobj -t %p/Inputs/trivial.obj.elf-i386 > %t.t
+RUN: cmp %t.symbols %t.t
+RUN: llvm-readelf -s -elf-output-style LLVM %p/Inputs/trivial.obj.elf-i386 > %t.lowers
+RUN: cmp %t.symbols %t.lowers
+
 COFF:      Symbols [
 COFF-NEXT:   Symbol {
 COFF-NEXT:     Name: @comp.id