the allowed CPPFLAGS, CXXFLAGS, FFLAGS, and LDFLAGS.

Also for security reasons, only a limited set of characters are
permitted, notably alphanumeric characters and a few symbols, such as
'.', that will not be interpreted in unexpected ways. Attempts to use
forbidden characters will get a "malformed #cgo argument" error.

When building, the CGO_CFLAGS, CGO_CPPFLAGS, CGO_CXXFLAGS, CGO_FFLAGS and

	// Use ReadSlice to look for delim, accumulating full buffers.
	for {
		var e error
		frag, e = b.ReadSlice(delim)
		if e == nil { // got final fragment
			break
		}
		if e != ErrBufferFull { // unexpected error
			err = e
			break
		}

		// Make a copy of the buffer.
		buf := bytes.Clone(frag)
		fullBuffers = append(fullBuffers, buf)
		totalLen += len(buf)
	}

	totalLen += len(frag)

      EXPECT_FALSE(found_scalar_const);
      found_scalar_const = true;
    } else if (IsAddN(n, 2)) {
      EXPECT_FALSE(found_add);
      found_add = true;
    } else {
      ADD_FAILURE() << "Unexpected NodeDef: " << n.DebugString();
    }
  }
  EXPECT_TRUE(found_placeholder);
  EXPECT_TRUE(found_scalar_const);
  EXPECT_TRUE(found_add);

  // Add another oper to the graph.

        with `--copt=/experimental:preprocessor
        --host_copt=/experimental:preprocessor` (see `.bazelrc` for more
        details). Builds including TensorFlow may fail with unexpected syntax
        errors if these flags are absent. See also
        [this thread on SIG Build](https://groups.google.com/a/tensorflow.org/g/build/c/LbAw8RILvTg/m/ttnuhYU2BgAJ).

## Known Caveats

pkg regexp/syntax, const ErrMissingRepeatArgument = "missing argument to repetition operator"
pkg regexp/syntax, const ErrTrailingBackslash = "trailing backslash at end of expression"
pkg regexp/syntax, const ErrUnexpectedParen = "unexpected )"
pkg regexp/syntax, const ErrUnexpectedParen ErrorCode
pkg regexp/syntax, const FoldCase = 1
pkg regexp/syntax, const InstAlt = 0
pkg regexp/syntax, const InstAltMatch = 1