[llvm-objdump] -p: Dump PE header for PE/COFF

For a trivial DLL built with `clang --target=x86_64-windows -O2 -c a.c; lld-link -subsystem:console -dll a.o -out:a.dll`,
`objdump -p` vs `llvm-objdump -p`:

```
-a.dll:     file format pei-x86-64
-
+a.dll: file format coff-x86-64
 Characteristics 0x2022
        executable
        large address aware
@@ -57,4 +56,4 @@
 Entry d 0000000000000000 00000000 Delay Import Directory
 Entry e 0000000000000000 00000000 CLR Runtime Header
 Entry f 0000000000000000 00000000 Reserved
-
+Export Table:
```

For a Linux image (`vmlinuz-5.10.76-gentoo-r1`) built with `CONFIG_EFI_STUB=y`

```
-vmlinuz-5.10.76-gentoo-r1:     file format pei-x86-64
-
-Characteristics 0x20e
+vmlinuz-5.10.76-gentoo-r1:     file format coff-x86-64
+Characteristics 0x206
        executable
        line numbers stripped
-       symbols stripped
        debugging information removed

 Time/Date              Wed Dec 31 16:00:00 1969
@@ -55,10 +53,4 @@
 Entry d 0000000000000000 00000000 Delay Import Directory
 Entry e 0000000000000000 00000000 CLR Runtime Header
 Entry f 0000000000000000 00000000 Reserved
-
-
-PE File Base Relocations (interpreted .reloc section contents)
-
-Virtual Address: 000037ca Chunk size 10 (0xa) Number of fixups 1
-       reloc    0 offset    0 [37ca] ABSOLUTE
-
+Export Table:
```

`symbols stripped` looks like a GNU objdump problem.

Reviewed By: jhenderson, alexander-shaposhnikov

Differential Revision: https://reviews.llvm.org/D113356