astro/gpstk: Fix patches and CMake build

After the last commit to this port [1], that updated DISTFILES, patch
errors were reported on pkg-fallout:

patch: **** can't cd to /wrkdirs/usr/ports/astro/gpstk/work/dev: No such file or directory
=> Patch patch-ext__lib__FileDirProc__FileHunter.cpp failed to apply cleanly.
*** Error code 1

This change replaces a WRKSRC override with a CMAKE_SOURCE_PATH
variable to declare the source directory and regenerates patchfiles
against the default WRKSRC.

While I'm here: switch to USES=cmake:outsource to match the build
instructions upstream [2]

It was also noted during testing that this port builds with the base
Clang c++ compiler and does not require USE_GCC. Upstream documentation
requires only 'a modern, ANSI compliant C++ compiler' [3]

[1] https://svnweb.freebsd.org/changeset/ports/399654
[2] http://www.gpstk.org/bin/view/Documentation/BuildingGPSTkUnderUnix
[3] http://www.gpstk.org/bin/view/Documentation/SystemRequirements

PR:		201196
MFH:		2015Q4

astro/gpstk/Makefile

@@ -12,12 +12,12 @@ COMMENT=	Toolkit for developing GPS applications
 
 LICENSE=	LGPL3
 
-USES=		cmake python:run
+USES=		cmake:outsource python:run
 USE_GCC=	yes
 USE_LDCONFIG=	yes
 
+CMAKE_SOURCE_PATH=	${WRKSRC}/dev
+
 EXTRACT_AFTER_ARGS=	--exclude .git
 
-WRKSRC=		${WRKDIR}/dev
-
 .include <bsd.port.mk>

astro/gpstk/files/patch-dev_ext_lib_FileDirProc_FileHunter.cpp

@@ -0,0 +1,10 @@
+--- dev/ext/lib/FileDirProc/FileHunter.cpp.orig	2014-10-10 19:46:15 UTC
++++ dev/ext/lib/FileDirProc/FileHunter.cpp
+@@ -52,6 +52,7 @@ using namespace gpstk::StringUtils;
+ #ifndef _WIN32
+ #include <unistd.h>
+ #include <dirent.h>
++#include <sys/syslimits.h>
+ #else
+ #include <io.h>
+ #include <direct.h>

astro/gpstk/files/patch-dev_ext_lib_Utilities_BinUtils.hpp

@@ -1,5 +1,5 @@
---- ext/lib/Utilities/BinUtils.hpp.orig	2014-10-11 11:19:24 UTC
-+++ ext/lib/Utilities/BinUtils.hpp
+--- dev/ext/lib/Utilities/BinUtils.hpp.orig	2014-10-10 19:46:16 UTC
++++ dev/ext/lib/Utilities/BinUtils.hpp
 @@ -54,6 +54,7 @@
  
  #include "Exception.hpp"

astro/gpstk/files/patch-ext__lib__FileDirProc__FileHunter.cpp

@@ -1,10 +0,0 @@
---- ext/lib/FileDirProc/FileHunter.cpp.orig	2014-10-10 19:46:15 UTC
-+++ ext/lib/FileDirProc/FileHunter.cpp
-@@ -52,6 +52,7 @@
- #ifndef _WIN32
- #include <unistd.h>
- #include <dirent.h>
-+#include <sys/syslimits.h>
- #else
- #include <io.h>
- #include <direct.h>