[lld] Support RUN_LLD_MAIN_TWICE for the ELF port

This enables the LLD_IN_TEST=2 testing mode for
```
path/to/llvm-lit -sv --param RUN_LLD_MAIN_TWICE=1 lld/test/ELF
```

When `Fatal` is called, `RunSafely` will return false.
For the first invocation in LLD_IN_TEST=2 mode, `inTestOutputDisabled`
is true and lld will not write to stdout/stderr, making many tests fail.
(This essentially discourages `Fatal` calls in the source code.)

Add XFAIL: main-run-twice to these tests similar to
https://reviews.llvm.org/D112898 for Mach-O

```
xargs </tmp/0 sed -Ei '1s/(;|#|\/\/) REQUIRES: .*/\0\n\1 XFAIL: main-run-twice/;t;1s/^/# XFAIL: main-run-twice\n/'
```

Author: MaskRay

lld/test/ELF/archive-thin-missing-member.s

@@ -1,4 +1,5 @@
 # REQUIRES: x86
+# XFAIL: main-run-twice
 
 # RUN: rm -f %t-no-syms.a
 # RUN: rm -f %t-syms.a

lld/test/ELF/arm-thumb-thunk-v6m-xo.s

@@ -1,4 +1,5 @@
 // REQUIRES: arm
+// XFAIL: main-run-twice
 // RUN: rm -rf %t && split-file %s %t
 // RUN: llvm-mc -arm-add-build-attributes -filetype=obj -triple=armv6m-none-eabi %t/a.s -o %t/a.o
 // RUN: ld.lld --no-rosegment --script %t/a.t %t/a.o -o %t/a

lld/test/ELF/arm-thunk-section-too-large.s

@@ -1,4 +1,5 @@
 // REQUIRES: arm
+// XFAIL: main-run-twice
 // RUN: llvm-mc %s -triple=armv7a-linux-gnueabihf -arm-add-build-attributes -filetype=obj -o %t.o
 // RUN: not ld.lld %t.o -o /dev/null 2>&1 | FileCheck %s
 

lld/test/ELF/arm-thunk-toolargesection.s

@@ -1,4 +1,5 @@
 // REQUIRES: arm
+// XFAIL: main-run-twice
 // RUN: llvm-mc -filetype=obj -triple=thumbv7a-none-linux-gnueabi %s -o %t
 // RUN: not ld.lld %t -o /dev/null 2>&1 | FileCheck %s
 

lld/test/ELF/arm-v5-reloc-error.s

@@ -1,4 +1,5 @@
 // REQUIRES: arm
+// XFAIL: main-run-twice
 // RUN: llvm-mc -filetype=obj -triple=armv7a-linux-gnueabi %s -o %t
 // RUN: echo "SECTIONS { \
 // RUN:       . = SIZEOF_HEADERS; \

lld/test/ELF/bad-archive.s

@@ -1,4 +1,5 @@
 // REQUIRES: x86
+// XFAIL: main-run-twice
 
 // Check bad archive error reporting with --whole-archive
 // and without it.

lld/test/ELF/fatlto/fatlto.invalid.s

@@ -1,4 +1,5 @@
 # REQUIRES: x86
+# XFAIL: main-run-twice
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
 # RUN: not ld.lld %t -o /dev/null --fat-lto-objects 2>&1 | FileCheck %s
 

lld/test/ELF/invalid-cie-reference.s

@@ -1,4 +1,5 @@
 // REQUIRES: x86
+// XFAIL: main-run-twice
 
 // RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t
 // RUN: not ld.lld %t -o /dev/null 2>&1 | FileCheck %s

lld/test/ELF/invalid/comdat-broken.test

@@ -1,4 +1,5 @@
 # REQUIRES: x86
+# XFAIL: main-run-twice
 
 # RUN: yaml2obj %s -o %t.o
 # RUN: not ld.lld %t.o -o /dev/null 2>&1 | FileCheck %s

lld/test/ELF/invalid/common-symbol-alignment.test

@@ -1,3 +1,4 @@
+# XFAIL: main-run-twice
 ## If an object contains a common symbol with zero alignment,
 ## check we report it.
 # RUN: yaml2obj --docnum=1 %s -o %t1.o

lld/test/ELF/invalid/data-encoding.test

@@ -1,4 +1,5 @@
 # REQUIRES: x86
+# XFAIL: main-run-twice
 
 # The object in the archive has invalid data encoding.
 # Check we report this.

lld/test/ELF/invalid/dynamic-section-broken.test

@@ -1,3 +1,4 @@
+# XFAIL: main-run-twice
 ## .dynamic section has invalid sh_entsize, check we report it.
 # RUN: yaml2obj --docnum=1 %s -o %t.so
 # RUN: not ld.lld %t.so -o /dev/null 2>&1 | FileCheck %s --check-prefix=ERR1

lld/test/ELF/invalid/invalid-elf.test

@@ -1,3 +1,4 @@
+# XFAIL: main-run-twice
 # RUN: rm -rf %t && mkdir -p %t
 # RUN: echo > %t/empty.o
 # RUN: llvm-ar --format=gnu cr %t/not-elf.a %t/empty.o

lld/test/ELF/invalid/invalid-file-class.test

@@ -1,4 +1,5 @@
 # REQUIRES: x86
+# XFAIL: main-run-twice
 # RUN: rm -rf %t && mkdir -p %t
 
 ## In this test, we check that able to report objects with

lld/test/ELF/invalid/invalid-soname.test

@@ -1,4 +1,5 @@
 # REQUIRES: x86
+# XFAIL: main-run-twice
 # RUN: yaml2obj %s -o %t.so
 # RUN: not ld.lld %t.so -o /dev/null 2>&1 | FileCheck %s
 

lld/test/ELF/invalid/sht-group-wrong-section.test

@@ -1,4 +1,5 @@
 # REQUIRES: x86
+# XFAIL: main-run-twice
 # RUN: yaml2obj %s -o %t.o
 # RUN: not ld.lld %t.o %t.o -o /dev/null 2>&1 | FileCheck %s
 # CHECK: error: {{.*}}.o: invalid section index in group: 12345

lld/test/ELF/invalid/sht-group.test

@@ -1,4 +1,5 @@
 # REQUIRES: x86
+# XFAIL: main-run-twice
 # RUN: yaml2obj %s -o %t.o
 # RUN: not ld.lld %t.o -o /dev/null 2>&1 | FileCheck %s
 # CHECK: invalid symbol index

lld/test/ELF/invalid/symtab-sh-info.s

@@ -1,3 +1,4 @@
+# XFAIL: main-run-twice
 ## .symtab's sh_info contains zero value. First entry in a .symtab is a
 ## zero entry that must exist in a valid object, so sh_info can't be null.
 ## Check we report a proper error for that case.

lld/test/ELF/invalid/verneed-shared.test

@@ -1,4 +1,5 @@
 ## REQUIRES: x86
+# XFAIL: main-run-twice
 ## Test that we can parse SHT_GNU_verneed in a shared object and report certain errors.
 
 # RUN: echo '.globl _start; _start:' | llvm-mc -filetype=obj -triple=x86_64 - -o %t.o

lld/test/ELF/lto/bitcode-nodatalayout.ll

@@ -1,4 +1,5 @@
 ; REQUIRES: x86
+; XFAIL: main-run-twice
 ; RUN: llvm-as %s -o %t.o
 ; RUN: not ld.lld %t.o -o /dev/null 2>&1 | FileCheck %s
 

lld/test/ELF/lto/bitcode-wrapper.ll

@@ -1,4 +1,5 @@
 ; REQUIRES: x86
+; XFAIL: main-run-twice
 
 ;; The LLVM bitcode format allows for an optional wrapper header. This test
 ;; shows that LLD can handle bitcode wrapped in this way, and also that an

lld/test/ELF/unsupported-emachine.test

@@ -1,3 +1,4 @@
+# XFAIL: main-run-twice
 # RUN: yaml2obj %s -o %t.o
 # RUN: not ld.lld %t.o -o /dev/null 2>&1 | FileCheck %s
 

lld/test/lit.cfg.py

@@ -104,8 +104,6 @@
     config.environment["LLD_IN_TEST"] = "1"
 else:
     config.environment["LLD_IN_TEST"] = "2"
-    # Many ELF tests fail in this mode.
-    config.excludes.append("ELF")
     # Some old Mach-O backend tests fail, and it's due for removal anyway.
     config.excludes.append("mach-o")
     # Some new Mach-O backend tests fail; give them a way to mark themselves