LLVMDependencyConfigTool fails with exception if llvm-config --shared-mode returns in error

[ydirson]

While configuring mesa for cross-compiling I hit the following stack trace (with 0.53.2):

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| Checking for function "strtof" : YES
| Checking for function "mkostemp" : YES
| Traceback (most recent call last):
|   File ".../mesonbuild/mesonmain.py", line 129, in run
|     return options.run_func(options)
|   File ".../mesonbuild/msetup.py", line 245, in run
|     app.generate()
|   File ".../mesonbuild/msetup.py", line 159, in generate
|     self._generate(env)
|   File ".../mesonbuild/msetup.py", line 192, in _generate
|     intr.run()
|   File ".../mesonbuild/interpreter.py", line 4168, in run
|     super().run()
|   File ".../mesonbuild/interpreterbase.py", line 412, in run
|     self.evaluate_codeblock(self.ast, start=1)
|   File ".../mesonbuild/interpreterbase.py", line 436, in evaluate_codeblock
|     raise e
|   File ".../mesonbuild/interpreterbase.py", line 430, in evaluate_codeblock
|     self.evaluate_statement(cur)
|   File ".../mesonbuild/interpreterbase.py", line 451, in evaluate_statement
|     return self.evaluate_if(cur)
|   File ".../mesonbuild/interpreterbase.py", line 530, in evaluate_if
|     self.evaluate_codeblock(i.block)
|   File ".../mesonbuild/interpreterbase.py", line 436, in evaluate_codeblock
|     raise e
|   File ".../mesonbuild/interpreterbase.py", line 430, in evaluate_codeblock
|     self.evaluate_statement(cur)
|   File ".../mesonbuild/interpreterbase.py", line 443, in evaluate_statement
|     return self.assignment(cur)
|   File ".../mesonbuild/interpreterbase.py", line 1064, in assignment
|     value = self.evaluate_statement(node.value)
|   File ".../mesonbuild/interpreterbase.py", line 441, in evaluate_statement
|     return self.function_call(cur)
|   File ".../mesonbuild/interpreterbase.py", line 788, in function_call
|     return func(node, posargs, kwargs)
|   File ".../mesonbuild/interpreterbase.py", line 285, in wrapped
|     return f(*wrapped_args, **wrapped_kwargs)
|   File ".../mesonbuild/interpreterbase.py", line 285, in wrapped
|     return f(*wrapped_args, **wrapped_kwargs)
|   File ".../mesonbuild/interpreterbase.py", line 285, in wrapped
|     return f(*wrapped_args, **wrapped_kwargs)
|   [Previous line repeated 2 more times]
|   File ".../mesonbuild/interpreterbase.py", line 155, in wrapped
|     ret = f(*wrapped_args, **wrapped_kwargs)
|   File ".../mesonbuild/interpreterbase.py", line 174, in wrapped
|     return f(*wrapped_args, **wrapped_kwargs)
|   File ".../mesonbuild/interpreter.py", line 3237, in func_dependency
|     d = self.dependency_impl(name, display_name, kwargs)
|   File ".../mesonbuild/interpreter.py", line 3284, in dependency_impl
|     dep = dependencies.find_external_dependency(name, self.environment, kwargs)
|   File ".../mesonbuild/dependencies/base.py", line 2237, in find_external_dependency
|     d = c()
|   File ".../mesonbuild/dependencies/dev.py", line 239, in __init__
|     self._set_new_link_args(environment)
|   File ".../mesonbuild/dependencies/dev.py", line 287, in _set_new_link_args
|     mode = self.get_config_value(['--shared-mode'], 'link_args')[0]
| IndexError: list index out of range

Turns out llvm-config --shared-mode fails (separate issue, https://bugzilla.yoctoproject.org/show_bug.cgi?id=13937), but meson should catch the error and notify the user of the llvm-config failure.