Update ELF FileHeder Flags field in a few tests

Author: aakanksha555

llvm/test/tools/llvm-objcopy/ELF/cross-arch-headers.test

@@ -127,6 +127,7 @@ FileHeader:
   Data:            ELFDATA2LSB
   Type:            ET_EXEC
   # Arbitrary values that do not match any value we convert to via --output-format.
+  Machine:         EM_NONE
   OSABI:           ELFOSABI_STANDALONE
 Sections:
   - Name:            .text

llvm/test/tools/llvm-objcopy/MachO/remove-swift-symbols.test

@@ -112,7 +112,7 @@ FileHeader:
   filetype:        0x00000002
   ncmds:           4
   sizeofcmds:      400
-  flags:           [[FLAGS]]
+  flags:           [[FLAGS=<none>]]
   reserved:        0x00000000
 LoadCommands:
   - cmd:             LC_SEGMENT_64

llvm/test/tools/obj2yaml/ELF/mips-eflags.yaml

@@ -274,6 +274,7 @@ FileHeader:
   Data:    ELFDATA2LSB
   Type:    ET_REL
   Machine: EM_MIPS
+  Flags:   [ ]
 
 # RUN: yaml2obj --docnum=26 %s -o %t-arch-2
 # RUN: obj2yaml %t-arch-2 | FileCheck %s -DARCH=EF_MIPS_ARCH_2 --check-prefix=ARCH