pgsql: Fix Perl coding error in msvc build system

Fix Perl coding error in msvc build system

Code like

    open(P, "cl /? 2>&1 |") || die "cl command not found";

does not actually catch any errors, because the exit status of the
command before the pipe is ignored.  The fix is to look at $?.

This also gave the opportunity to clean up the logic of this code a bit.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/d30292b8c45a1d909ff7d84bd6787c8827134fc3

Modified Files
--------------
src/tools/msvc/Solution.pm        |   14 +++-----------
src/tools/msvc/VSObjectFactory.pm |   28 +++++++---------------------
2 files changed, 10 insertions(+), 32 deletions(-)