[llvm-objcopy] Add --strip-all-gnu and change --strip-all

GNU's --strip-all doesn't strip as aggressively as it could in general.
Currently llvm-objcopy copies the exact behavoir of GNU's --strip-all.
eu-strip is used as a drop in replacement for GNU strip/objcopy in many many
places without issue. eu-strip removes non-allocated sections and keeps
.gnu.warning* sections. Because --strip-all will likely be the most widely
used stripping option we should make --strip-all as aggressive as it can safely
be. Since we have evidence from eu-strip that this is a safe option we should
allow it. For those that might still have an issue afterwards I've added
--strip-all-gnu as an exact drop in replacement for GNU's --strip-all as well.

llvm-svn: 319071
diff --git a/llvm/test/tools/llvm-objcopy/strip-all-gnu.test b/llvm/test/tools/llvm-objcopy/strip-all-gnu.test
new file mode 100644
index 0000000..48d34e8
--- /dev/null
+++ b/llvm/test/tools/llvm-objcopy/strip-all-gnu.test
@@ -0,0 +1,54 @@
+# RUN: yaml2obj %s > %t
+# RUN: llvm-objcopy --strip-all-gnu %t %t2
+# RUN: llvm-readobj -file-headers -sections %t2 | FileCheck %s
+
+!ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_REL
+  Machine:         EM_X86_64
+Sections:
+  - Name:            .dynstr
+    Type:            SHT_STRTAB
+    Flags:           [ SHF_ALLOC ]
+  - Name:            .symtab.dyn
+    Type:            SHT_SYMTAB
+    Flags:           [ SHF_ALLOC ]
+    Type:            SHT_NOBITS
+  - Name:            .text
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+    Size:            4
+  - Name:            .debug_info
+    Type:            SHT_PROGBITS
+    Flags:           [ ]
+    AddressAlign:    0x1
+    Size:            4
+  - Name:            .debug_loc
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC ]
+    AddressAlign:    0x1
+    Size:            4
+  - Name:            .comment
+    Type:            SHT_PROGBITS
+  - Name:            .random_section_name
+    Type:            SHT_PROGBITS
+  - Name:            .debug_not_a_real_debug_section
+    Type:            SHT_PROGBITS
+  - Name:            .rel.text
+    Type:            SHT_REL
+    Info:            .text
+  - Name:            .rela.text
+    Type:            SHT_RELA
+    Info:            .text
+
+# CHECK: SectionHeaderCount: 8
+
+# CHECK:      Name: .dynstr
+# CHECK:      Name: .symtab.dyn
+# CHECK:      Name: .text
+# CHECK:      Name: .debug_loc
+# CHECK:      Name: .comment
+# CHECK:      Name: .random_section_name
+# CHECK:      Name: .shstrtab