[MC,test] Reorganize OSABI tests

Author: MaskRay

llvm/test/MC/AArch64/elf_osabi_flags.s

@@ -0,0 +1,12 @@
+# REQUIRES: aarch64-registered-target
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s | llvm-readobj -h - | \
+# RUN:   FileCheck %s --check-prefix=SYSV
+# SYSV: OS/ABI: SystemV
+
+# RUN: llvm-mc -filetype=obj -triple=amd64-solaris %s | llvm-readobj -h - | \
+# RUN:   FileCheck %s --check-prefix=SOLARIS
+# SOLARIS: OS/ABI: Solaris
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-freebsd %s | llvm-readobj -h - | \
+# RUN:   FileCheck %s --check-prefix=FREEBSD
+# FREEBSD: OS/ABI: FreeBSD