fully exploited the dropped support of LLVM 8

This commit grepped for LLVM_VERSION_GE, LLVM_VERSION_LT, get_major_version and
min-llvm-version and statically evaluated every expression possible
(and sensible) assuming that the LLVM version is >=9 now

src/test/codegen/abi-efiapi.rs

@@ -1,7 +1,6 @@
 // Checks if the correct annotation for the efiapi ABI is passed to llvm.
 
 // revisions:x86_64 i686 aarch64 arm riscv
-// min-llvm-version: 9.0
 // needs-llvm-components: aarch64 arm riscv
 
 //[x86_64] compile-flags: --target x86_64-unknown-uefi

src/test/codegen/force-unwind-tables.rs

@@ -1,4 +1,3 @@
-// min-llvm-version: 8.0
 // compile-flags: -C no-prepopulate-passes -C force-unwind-tables=y
 
 #![crate_type="lib"]

src/test/ui/sanitize/new-llvm-pass-manager-thin-lto.rs

@@ -2,7 +2,6 @@
 // being run when compiling with new LLVM pass manager and ThinLTO.
 // Note: The issue occurred only on non-zero opt-level.
 //
-// min-llvm-version: 9.0
 // needs-sanitizer-support
 // needs-sanitizer-address
 //