[BOLT][test] Enable cross-target testing

Check for supported target architecture instead of the host arch when
deciding to execute non-runtime tests.

Reviewed By: Amir

Differential Revision: https://reviews.llvm.org/D122498

Author: maksfb

bolt/test/AArch64/lit.local.cfg

@@ -1,4 +1,4 @@
-if config.host_arch not in ['aarch64']:
+if 'AArch64' not in config.root.targets:
     config.unsupported = True
 
 config.substitutions.insert(

bolt/test/X86/lit.local.cfg

@@ -1,4 +1,4 @@
-if config.host_arch not in ['x86', 'X86', 'x86_64']:
+if not 'X86' in config.root.targets:
     config.unsupported = True
 
 config.substitutions.insert(

bolt/test/lit.cfg.py

@@ -102,3 +102,5 @@ def calculate_arch_features(arch_string):
      ('--cxxflags', {r'-D_GLIBCXX_DEBUG\b': 'libstdcxx-safe-mode'}),
         ('--targets-built', calculate_arch_features)
      ])
+
+config.targets = frozenset(config.targets_to_build.split())

bolt/test/lit.site.cfg.py.in

@@ -21,6 +21,7 @@ config.enable_abi_breaking_checks = "@LLVM_ENABLE_ABI_BREAKING_CHECKS@"
 config.python_executable = "@PYTHON_EXECUTABLE@"
 config.bolt_clang = "@BOLT_CLANG_EXE@"
 config.bolt_lld = "@BOLT_LLD_EXE@"
+config.targets_to_build = "@TARGETS_TO_BUILD@"
 
 import lit.llvm
 lit.llvm.initialize(lit_config, config)