[clang-format] Fix regression about short functions after #else

[krasimir]

Summary

This patch fixes a regression introduced in r312904, where the formatter confuses
the else in #else with an else of an if-else statement.
For example, formatting this code with google style

#ifdef A
int f() {}
#else
int f() {}
#endif

resulted in

#ifdef A
int f() {}
#else
int f() {
}
#endif

[sammccall]

This test looks like it was intended to catch some case, maybe we're now mishandling some case like

if (foo)
{
}
else
{
  // this can now be merged
}

But there's no testcase and I'm guessing, so let's fix the #else bug :-)

cfe/trunk/lib/Format/UnwrappedLineFormatter.cpp

tryMergeSimpleBlock(SmallVectorImpl<AnnotatedLine *>::const_iterator I,
     // line is added, change this to not return for @try and friends.
     if (Style.Language != FormatStyle::LK_Java &&
         Line.First->isOneOf(tok::at, tok::minus, tok::plus))
       return 0;
 
     // Check that the current line allows merging. This depends on whether we
     // are in a control flow statements as well as several style flags.
     if (Line.First->isOneOf(tok::kw_else, tok::kw_case) ||
-        (Line.First->Next && Line.First->Next->is(tok::kw_else)) ||
-        (I != AnnotatedLines.begin() && I[-1]->Last->is(tok::kw_else)))
+        (Line.First->Next && Line.First->Next->is(tok::kw_else)))
       return 0;
     if (Line.First->isOneOf(tok::kw_if, tok::kw_while, tok::kw_do, tok::kw_try,
                             tok::kw___try, tok::kw_catch, tok::kw___finally,
                             tok::kw_for, tok::r_brace, Keywords.kw___except)) {
       if (!Style.AllowShortBlocksOnASingleLine)
         return 0;
       // Don't merge when we can't except the case when
       // the control statement block is empty

cfe/trunk/unittests/Format/FormatTest.cpp

verifyFormat("int aaaaaaaaaaaaaa(int bbbbbbbbbbbbbb)\n"
                "{}",
                Style);
   verifyFormat("int aaaaaaaaaaaaaa(int bbbbbbbbbbbbbb)\n"
                "{\n"
                "  return 0;\n"
                "}",
                Style);
 }
+TEST_F(FormatTest, KeepShortFunctionAfterPPElse) {
+  FormatStyle Style = getLLVMStyle();
+  Style.AllowShortFunctionsOnASingleLine = FormatStyle::SFS_All;
+  verifyFormat("#ifdef A\n"
+               "int f() {}\n"
+               "#else\n"
+               "int g() {}\n"
+               "#endif",
+               Style);
+}
 
 TEST_F(FormatTest, SplitEmptyClass) {
   FormatStyle Style = getLLVMStyle();
   Style.BreakBeforeBraces = FormatStyle::BS_Custom;
   Style.BraceWrapping.AfterClass = true;
   Style.BraceWrapping.SplitEmptyRecord = false;
 
   verifyFormat("class Foo\n"