Use git submodule for gsl-lite

.gitmodules

@@ -1,3 +1,6 @@
 [submodule "vendor/pugixml"]
 	path = vendor/pugixml
 	url = https://github.com/zeux/pugixml.git
+[submodule "vendor/gsl-lite"]
+	path = vendor/gsl-lite
+	url = https://github.com/martinmoene/gsl-lite.git

CMakeLists.txt

@@ -133,15 +133,10 @@ target_link_libraries(xtensor INTERFACE xtl)
 # GSL header-only library
 #===============================================================================
 
-add_library(gsl INTERFACE)
-target_include_directories(gsl
-  INTERFACE
-    $<INSTALL_INTERFACE:include/gsl/include>
-    $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/vendor/gsl/include>
-)
+add_subdirectory(vendor/gsl-lite)
 
 # Make sure contract violations throw exceptions
-target_compile_definitions(gsl INTERFACE GSL_THROW_ON_CONTRACT_VIOLATION)
+target_compile_definitions(gsl-lite INTERFACE GSL_THROW_ON_CONTRACT_VIOLATION)
 
 #===============================================================================
 # RPATH information
@@ -321,7 +316,7 @@ endif()
 # target_link_libraries treats any arguments starting with - but not -l as
 # linker flags. Thus, we can pass both linker flags and libraries together.
 target_link_libraries(libopenmc ${ldflags} ${HDF5_LIBRARIES} ${HDF5_HL_LIBRARIES}
-                      pugixml faddeeva xtensor gsl)
+                      pugixml faddeeva xtensor gsl-lite)
 
 if(dagmc)
   target_compile_definitions(libopenmc PRIVATE DAGMC)
@@ -357,7 +352,7 @@ add_custom_command(TARGET libopenmc POST_BUILD
 #===============================================================================
 
 set(INSTALL_CONFIGDIR ${CMAKE_INSTALL_LIBDIR}/cmake/OpenMC)
-install(TARGETS openmc libopenmc pugixml faddeeva gsl
+install(TARGETS openmc libopenmc pugixml faddeeva gsl-lite
   EXPORT openmc-targets
   RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
   LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
@@ -376,7 +371,4 @@ install(DIRECTORY include/ DESTINATION ${CMAKE_INSTALL_INCLUDEDIR})
 
 # Copy headers for vendored dependencies (note that xtensor/xtl are handled
 # separately since they are managed by CMake)
-install(DIRECTORY vendor/pugixml DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
-  FILES_MATCHING PATTERN "*.hpp")
-install(DIRECTORY vendor/gsl DESTINATION ${CMAKE_INSTALL_INCLUDEDIR})
 install(DIRECTORY vendor/faddeeva DESTINATION ${CMAKE_INSTALL_INCLUDEDIR})

vendor/gsl-lite

@@ -0,0 +1 @@
+Subproject commit 93607223a48621dae3cedd6b3335431b38067fae

vendor/gsl/include/gsl/gsl

@@ -1,27 +0,0 @@
-//
-// gsl-lite is based on GSL: Guidelines Support Library.
-// For more information see https://github.com/martinmoene/gsl-lite
-//
-// Copyright (c) 2015 Martin Moene
-// Copyright (c) 2015 Microsoft Corporation. All rights reserved. 
-// 
-// This code is licensed under the MIT License (MIT). 
-// 
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 
-// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
-// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 
-// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 
-// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 
-// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN 
-// THE SOFTWARE. 
-
-// mimic MS include hierarchy
-
-#pragma once
-
-#ifndef GSL_GSL_H_INCLUDED
-#define GSL_GSL_H_INCLUDED
-
-#include "gsl-lite.hpp"
-
-#endif // GSL_GSL_H_INCLUDED