[BOLT][test] Use correct normalized triple

bolt/test/lit.local.cfg wants to use the system GCC installation but it
specifies a wrong triple ("linux" instead of "linux-gnu") and relies on
clangDriver's loose GCC installation detection to pick up "*-linux-gnu".

This loose behavior may not work. Use "linux-gnu" instead.

Note: neither "linux" nor "linux-gnu" detects "linux-musl" triples, so
these tests currently fail on musl based systems.

Other files changes are cosmetic.

Author: MaskRay

bolt/test/AArch64/lit.local.cfg

@@ -1,7 +1,7 @@
 if "AArch64" not in config.root.targets:
     config.unsupported = True
 
-flags = "--target=aarch64-pc-linux -nostartfiles -nostdlib -ffreestanding"
+flags = "--target=aarch64-unknown-linux-gnu -nostartfiles -nostdlib -ffreestanding"
 
 config.substitutions.insert(0, ("%cflags", f"%cflags {flags}"))
 config.substitutions.insert(0, ("%cxxflags", f"%cxxflags {flags}"))

bolt/test/X86/lit.local.cfg

@@ -1,7 +1,7 @@
 if not "X86" in config.root.targets:
     config.unsupported = True
 
-flags = "--target=x86_64-pc-linux -nostdlib"
+flags = "--target=x86_64-unknown-linux-gnu -nostdlib"
 
 config.substitutions.insert(0, ("%cflags", f"%cflags {flags}"))
 config.substitutions.insert(0, ("%cxxflags", f"%cxxflags {flags}"))

bolt/test/lit.local.cfg

@@ -1,4 +1,4 @@
-host_linux_triple = config.target_triple.split("-")[0] + "-linux"
+host_linux_triple = config.target_triple.split("-")[0] + "-unknown-linux-gnu"
 common_linker_flags = "-fuse-ld=lld -Wl,--unresolved-symbols=ignore-all"
 flags = f"--target={host_linux_triple} {common_linker_flags}"