Update CMake files for Emscripten support

Lower CMake version requirement to 3.22 and adjust `target_link_options` for Emscripten. Conditionalize `target_link_libraries` for Emscripten in both main and extras CMakeLists.

CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.28)
+cmake_minimum_required(VERSION 3.22)
 project(OasisC CXX C)
 
 add_subdirectory(libs/Oasis)
@@ -14,7 +14,7 @@ set(OasisC_SOURCES
 if (DEFINED EMSCRIPTEN)
     add_executable(OasisC ${OasisC_SOURCES})
     set(CMAKE_EXECUTABLE_SUFFIX ".mjs")
-    target_link_options(OasisC PUBLIC -sSINGLE_FILE --no-entry "-s EXPORT_NAME='OasisC'" "-s EXPORTED_RUNTIME_METHODS='[\"ccall\", \"cwrap\"]'")
+    target_link_options(OasisC PUBLIC -sSINGLE_FILE --no-entry "-sEXPORT_NAME='OasisC'" "-sEXPORTED_RUNTIME_METHODS=ccall,cwrap")
 else ()
     add_library(OasisC ${OasisC_SOURCES})
 endif ()
@@ -28,5 +28,7 @@ endif()
 
 if(OASIS_BUILD_EXTRAS)
     add_subdirectory(extras)
-    target_link_libraries(OasisC PUBLIC OasisCExtras)
+    if (DEFINED EMSCRIPTEN)
+        target_link_libraries(OasisC PUBLIC OasisCExtras)
+    endif ()
 endif()

extras/CMakeLists.txt

@@ -2,8 +2,12 @@ set(OasisC_EXTRAS_SOURCES
         # cmake-format: sortable
         src/FromString.cpp src/MathMLSerializer.cpp)
 
-add_library(OasisCExtras ${OasisC_EXTRAS_SOURCES})
-
+if (DEFINED EMSCRIPTEN)
+    add_library(OasisCExtras OBJECT ${OasisC_EXTRAS_SOURCES})
+else ()
+    add_library(OasisCExtras ${OasisC_EXTRAS_SOURCES})
+endif ()
+
 target_include_directories(OasisCExtras
         PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/include)
 target_link_libraries(OasisCExtras PUBLIC Oasis::Oasis Oasis::Extras)