Actually bundle libstdc++ statically

Turns out our static usearch library still depended on
the cpp runtime library libstdc++ dynamically.
This usually did not cause issues since postgres
commonly links libstdc++ dynamically so c++ symbols in our .so
would be resolved dynamically, when loaded.

This did cause issues for when postgres was not linked with
libstdc++. I do not know when exactly this happens but it seems
this at least happens when building postgres from source under
certain circumstances

This commit makes sure we actually bindule libstdc++ statically

c/CMakeLists.txt

@@ -64,11 +64,10 @@ set(USEARCH_PUNNED_INCLUDE_DIRS
 # This article discusses a better way to allow building either static or shared libraries
 # https://alexreinking.com/blog/building-a-dual-shared-and-static-library-with-cmake.html
 if (${USEARCH_BUILD_STATIC})
-    # apples does not understand -static-libstdc++ and cmake throws unused flag warning
-    if (NOT APPLE)
-        set(CMAKE_CXX_FLAGS " ${CMAKE_CXX_FLAGS} -static-libstdc++")
-    endif()
     add_library(usearch_c STATIC lib.cpp)
+    # Note: -static-libstdc++ is only meaningful for dynamic builds
+    # to bundle up the c++ standard library, we need to explicitly link it as below
+    target_link_libraries(usearch_c PRIVATE "libstdc++.a")
 else ()
     add_library(usearch_c SHARED lib.cpp)
 endif()