Fix tests on systems that do not have clang installed

pycheribuild/projects/project.py

@@ -1029,18 +1029,17 @@ def add_lto_build_options(self, ccinfo: CompilerInfo) -> bool:
                 return False
             ld = lld if self.lto_set_ld else None
             self.set_lto_binutils(ar=llvm_ar, ranlib=llvm_ranlib, nm=llvm_nm, ld=ld)
-        if self.prefer_full_lto_over_thin_lto:
+        if self.prefer_full_lto_over_thin_lto or not self.can_use_thinlto(ccinfo):
             self._lto_compiler_flags.append("-flto")
             self._lto_linker_flags.append("-flto")
         else:
             self._lto_compiler_flags.append("-flto=thin")
             self._lto_linker_flags.append("-flto=thin")
-            if self.can_use_lld(ccinfo.path):
-                thinlto_cache_flag = "--thinlto-cache-dir="
-            else:
+            if ccinfo.compiler == "apple-clang":
                 # Apple ld uses a different flag for the thinlto cache dir
-                assert ccinfo.compiler == "apple-clang"
                 thinlto_cache_flag = "-cache_path_lto,"
+            else:
+                thinlto_cache_flag = "--thinlto-cache-dir="
             self._lto_linker_flags.append("-Wl," + thinlto_cache_flag + str(self.build_dir / "thinlto-cache"))
         if self.compiling_for_cheri_hybrid([CPUArchitecture.AARCH64]):
             # Hybrid flags are not inferred from the input files, so we have to explicitly pass -mattr= to ld.lld.

tests/test_argument_parsing.py

@@ -1061,11 +1061,17 @@ def enable_projects_flag(args: "list[str]"):
         "llvm-native", config, BuildCheriLLVM).configure_args) == "-DLLVM_ENABLE_PROJECTS=llvm"
 
 
-def test_llvm_lto_options():
-    config = _parse_arguments(["--llvm/use-lto"])
+@pytest.mark.parametrize("args", [
+    pytest.param([], id="default-compiler"),
+    pytest.param(["--cc-path=/usr/bin/gcc"], id="gcc"),
+    pytest.param(["--cc-path=/this/compiler/does/not/exist"], id="invalid"),
+])
+def test_llvm_lto_options(args: "list[str]"):
+    config = _parse_arguments(["--llvm/use-lto", *args])
     llvm = _get_target_instance("llvm-native", config, BuildCheriLLVM)
-    # depending on the host compiler we could be using ThinLTO (if supported) or full LTO.
-    assert "-DLLVM_ENABLE_LTO=Thin" in llvm.configure_args or "-DLLVM_ENABLE_LTO=TRUE" in llvm.configure_args
+    if config.clang_path.exists():
+        # depending on the host compiler we could be using ThinLTO (if supported) or full LTO.
+        assert "-DLLVM_ENABLE_LTO=Thin" in llvm.configure_args or "-DLLVM_ENABLE_LTO=TRUE" in llvm.configure_args
     args_containing_flto = [x for x in llvm.configure_args if "_FLAGS_INIT=" in x and "-flto" in x]
     # The LLVM build system includes logic to set the correct LTO flags. It also avoids building tests with LTO to
     # reduce the build time. Explicitly adding the CFLAGS/LDFLAGS here breaks this optimization.