Provide 1 .hpp + 1 .cpp distribution of Catch2

This commits also adds a script that does the amalgamation of headers
and .cpp files into the distributable version, removes the old
`generateSingleHeader` script, and also adds a very simple compilation
test for the amalgamated distribution.

tests/ExtraTests/CMakeLists.txt

@@ -203,3 +203,24 @@ endforeach()
 list(FILTER EXTRA_TEST_BINARIES EXCLUDE REGEX "DisabledExceptions.*")
 list(APPEND CATCH_WARNING_TARGETS ${EXTRA_TEST_BINARIES})
 set(CATCH_WARNING_TARGETS ${CATCH_WARNING_TARGETS} PARENT_SCOPE)
+
+
+# This sets up a one-off executable that compiles against the amalgamated
+# files, and then runs it for a super simple check that the amalgamated
+# files are usable.
+add_executable(AmalgamatedTestCompilation
+  ${TESTS_DIR}/X91-AmalgamatedCatch.cpp
+  ${CATCH_DIR}/extras/catch_amalgamated.hpp
+  ${CATCH_DIR}/extras/catch_amalgamated.cpp
+)
+target_include_directories(AmalgamatedTestCompilation PRIVATE ${CATCH_DIR}/extras)
+set_property( TARGET AmalgamatedTestCompilation PROPERTY CXX_STANDARD 14 )
+set_property( TARGET AmalgamatedTestCompilation PROPERTY CXX_STANDARD_REQUIRED ON )
+set_property( TARGET AmalgamatedTestCompilation PROPERTY CXX_EXTENSIONS OFF )
+
+add_test(NAME AmalgamatedFileTest COMMAND AmalgamatedTestCompilation)
+set_tests_properties(
+    AmalgamatedFileTest
+  PROPERTIES
+    PASS_REGULAR_EXPRESSION "All tests passed \\(14 assertions in 3 test cases\\)"
+)

tests/ExtraTests/X91-AmalgamatedCatch.cpp

@@ -0,0 +1,31 @@
+/**\file
+ *
+ * This file serves as a simple compilation test against the amalgamated
+ * version of Catch2.
+ */
+
+#include "catch_amalgamated.hpp"
+
+TEST_CASE("Just a dummy test") {
+    auto i = GENERATE(1, 2, 3);
+    SECTION("a") {
+        REQUIRE(1 != 4);
+    }
+    SECTION("b") {
+        CHECK(1 != 5);
+    }
+    REQUIRE_THAT(1,
+                 Catch::Matchers::Predicate<int>([](int i) {
+                     return i % 2 == 1;
+                 }));
+}
+
+TEMPLATE_TEST_CASE("Trivial template test case", "", char, short) {
+    STATIC_REQUIRE(sizeof(TestType) <= sizeof(int));
+}
+
+TEST_CASE("Benchmark test", "[!benchmark]") {
+    BENCHMARK("Allocation benchmark") {
+        return std::vector<int>(10);
+    };
+}