same as 3f7c8ce1 for gcc_linux_x86-64 (see there
for a more detailed commit message; plus trivial follow-up
5e048869 "Remove spurious vertical whitespace").
Except use labels 'Lpush', 'Lpushed' not starting with a dot ('.Lpush',
'.Lpushed'), as otherwise at least macOS 10.12.1 linker (ld64-274.1), when
building libgcc3_uno.dylib's __TEXT,__unwind_info section, would use
callvirtualmethod.o's __LD,__compact_unwind entry---covering the complete
callVirtualMethod function---only for the first part of the function up to the
.Lpush label, and would mark the remainder as having no unwind information (a
compact_unwind_encoding_t value of 0; see the inline comments in the
libunwind-35.3 source code,
<http://opensource.apple.com/source/libunwind/libunwind-35.3/>).  So if an
exception shall pass through that latter part it would lead to std::terminate.

Change-Id: Ib1e8a5e4534b11ebe96c3ce774f8e5e8d45476cf