[test] Support git commit version ids for clang.

[rupprecht]

Summary

getCompilerVersion assumes that clang --version prints out a string like version [0-9\.]+.
If clang is built from trunk, the version line might look like clang version trunk (123abc).

Since there isn't any way of knowing by the commit id alone whether one commit is newer or older than another git commit (or clang version), assume that clang with a version id like this is very close to trunk. For example, any tests with @skipIf(compiler="clang", compiler_version=['<', '8']) should be run.

[MaskRay]

Thanks!

lldb/packages/Python/lldbsuite/test/lldbtest.py

def isIntelCompiler(self):
         """ Returns true if using an Intel (ICC) compiler, false otherwise. """
         return any([x in self.getCompiler() for x in ["icc", "icpc", "icl"]])
 
     def expectedCompilerVersion(self, compiler_version):
         """Returns True iff compiler_version[1] matches the current compiler version.
            Use compiler_version[0] to specify the operator used to determine if a match has occurred.
            Any operator other than the following defaults to an equality test:
              '>', '>=', "=>", '<', '<=', '=<', '!=', "!" or 'not'
+
+           If the current compiler version cannot be determined, we assume it is close to the top
+           of trunk, so any less-than or equal-to comparisons will return False, and any
+           greater-than or not-equal-to comparisons will return True.
         """
-        if (compiler_version is None):
+        if compiler_version is None:
             return True
         operator = str(compiler_version[0])
         version = compiler_version[1]
 
-        if (version is None):
+        if version is None:
             return True
-        if (operator == '>'):
-            return LooseVersion(self.getCompilerVersion()) > LooseVersion(version)
-        if (operator == '>=' or operator == '=>'):
-            return LooseVersion(self.getCompilerVersion()) >= LooseVersion(version)
-        if (operator == '<'):
-            return LooseVersion(self.getCompilerVersion()) < LooseVersion(version)
-        if (operator == '<=' or operator == '=<'):
-            return LooseVersion(self.getCompilerVersion()) <= LooseVersion(version)
-        if (operator == '!=' or operator == '!' or operator == 'not'):
-            return str(version) not in str(self.getCompilerVersion())
-        return str(version) in str(self.getCompilerVersion())
+
+        test_compiler_version = self.getCompilerVersion()
+        if test_compiler_version == 'unknown':
+            # Assume the compiler version is at or near the top of trunk.
+            return operator in ['>', '>=', '!', '!=', 'not']
+
+        if operator == '>':
+            return LooseVersion(test_compiler_version) > LooseVersion(version)
+        if operator == '>=' or operator == '=>':
+            return LooseVersion(test_compiler_version) >= LooseVersion(version)
+        if operator == '<':
+            return LooseVersion(test_compiler_version) < LooseVersion(version)
+        if operator == '<=' or operator == '=<':
+            return LooseVersion(test_compiler_version) <= LooseVersion(version)
+        if operator == '!=' or operator == '!' or operator == 'not':
+            return str(version) not in str(test_compiler_version)
+        return str(version) in str(test_compiler_version)
 
     def expectedCompiler(self, compilers):
         """Returns True iff any element of compilers is a sub-string of the current compiler."""
         if (compilers is None):
             return True
 
         for compiler in compilers:
             if compiler in self.getCompiler():