Merge commit '3bc509996b3f78980f4462393228d9f57e0b00c9' as 'third_party/GSL'

Change-Id: Idd4850195e2a433c2df378f7bc7f2d6d546ab3d1
diff --git a/third_party/GSL/.gitignore b/third_party/GSL/.gitignore
new file mode 100644
index 0000000..326971f
--- /dev/null
+++ b/third_party/GSL/.gitignore
@@ -0,0 +1,16 @@
+CMakeFiles
+build
+tests/CMakeFiles
+tests/Debug
+*.opensdf
+*.sdf
+tests/*tests.dir
+*.vcxproj
+*.vcxproj.filters
+*.sln
+*.tlog
+Testing/Temporary/*.*
+CMakeCache.txt
+*.suo
+.vs/
+.vscode/