[libfuzzer] Fix a test's run line

r342698 removed the 'UNSUPPORTED: windows' flags from a number of fuzzer
tests, however too many lines were removed from 'fuzzer-flags.test',
including the run-line that generates the test binary, which breaks that
test for me (and the clang-x64-ninja-win7 buildbot). This patch just
re-adds that line.

llvm-svn: 342720

compiler-rt/test/fuzzer/fuzzer-flags.test

@@ -1,3 +1,4 @@
+RUN: %cpp_compiler %S/FlagsTest.cpp -o %t-FlagsTest
 RUN: %run %t-FlagsTest -runs=10 -foo_bar=1 2>&1 | FileCheck %s --check-prefix=FOO_BAR
 FOO_BAR: WARNING: unrecognized flag '-foo_bar=1'; use -help=1 to list all flags
 FOO_BAR: BINGO