[lit]Add llvm-readelf to tool substitutions

[jhenderson]

Summary

llvm-readelf was missing from the list of tool substitutions in the lit configuration. This caused no functional issue, because the tools directory is also added to the PATH (why do we do both?), but it did mean that the lit output didn't provide the full path to the llvm-readelf executable, which is useful for rerunning the command outside the test.

[alexander-shaposhnikov]

oh, i see.

[rnk]

lgtm

test/lit.cfg.py

 # FIXME: Why do we have both `lli` and `%lli` that do slightly different things?
 tools.extend([
     'dsymutil', 'lli', 'lli-child-target', 'llvm-ar', 'llvm-as',
     'llvm-bcanalyzer', 'llvm-config', 'llvm-cov', 'llvm-cxxdump', 'llvm-cvtres',
     'llvm-diff', 'llvm-dis', 'llvm-dwarfdump', 'llvm-exegesis', 'llvm-extract',
     'llvm-isel-fuzzer', 'llvm-opt-fuzzer', 'llvm-lib', 'llvm-link', 'llvm-lto',
     'llvm-lto2', 'llvm-mc', 'llvm-mca', 'llvm-modextract', 'llvm-nm',
     'llvm-objcopy', 'llvm-objdump', 'llvm-pdbutil', 'llvm-profdata',
-    'llvm-ranlib', 'llvm-readobj', 'llvm-rtdyld', 'llvm-size', 'llvm-split',
-    'llvm-strings', 'llvm-strip', 'llvm-tblgen', 'llvm-undname', 'llvm-c-test',
-    'llvm-cxxfilt', 'llvm-xray', 'yaml2obj', 'obj2yaml', 'yaml-bench',
-    'verify-uselistorder', 'bugpoint', 'llc', 'llvm-symbolizer', 'opt',
-    'sancov', 'sanstats'])
+    'llvm-ranlib', 'llvm-readelf', 'llvm-readobj', 'llvm-rtdyld', 'llvm-size',
+    'llvm-split', 'llvm-strings', 'llvm-strip', 'llvm-tblgen', 'llvm-undname',
+    'llvm-c-test', 'llvm-cxxfilt', 'llvm-xray', 'yaml2obj', 'obj2yaml',
+    'yaml-bench', 'verify-uselistorder', 'bugpoint', 'llc', 'llvm-symbolizer',
+    'opt', 'sancov', 'sanstats'])
 
 # The following tools are optional
 tools.extend([
     ToolSubst('llvm-go', unresolved='ignore'),
     ToolSubst('llvm-mt', unresolved='ignore'),
     ToolSubst('Kaleidoscope-Ch3', unresolved='ignore'),
     ToolSubst('Kaleidoscope-Ch4', unresolved='ignore'),
     ToolSubst('Kaleidoscope-Ch5', unresolved='ignore'),