fix: Build iconfix as static library

On CI we build using the bundled Quazip, and automatically set
-DBUILD_STATIC_LIBS to true, so it build iconfix statically as well.

However, since we recently added support for using the system quazip,
this flag is not set anymore, and PolyMC fails to run because iconfix
neither is statically linked, nor it creates a .so file for dynamic
linking.

Since most other libs are built statically, we should make this one
static as well. Maybe we should consider allowing for dynamic linking of
libs now that quazip is not much of an issue anymore. :^)

libraries/iconfix/CMakeLists.txt

@@ -12,7 +12,7 @@ internal/qiconloader.cpp
 internal/qiconloader_p.h
 )
 
-add_library(Launcher_iconfix ${ICONFIX_SOURCES})
+add_library(Launcher_iconfix STATIC ${ICONFIX_SOURCES})
 target_include_directories(Launcher_iconfix PUBLIC ${CMAKE_CURRENT_SOURCE_DIR} "${CMAKE_CURRENT_BINARY_DIR}" )
 
 target_link_libraries(Launcher_iconfix Qt5::Core Qt5::Widgets)