Use default cpp fmt build script.

vendor/Fmt/test/static-export-test/CMakeLists.txt

@@ -0,0 +1,30 @@
+cmake_minimum_required(VERSION 3.1...3.18)
+
+project(fmt-link CXX)
+
+set(BUILD_SHARED_LIBS OFF)
+set(CMAKE_VISIBILITY_INLINES_HIDDEN TRUE)
+set(CMAKE_CXX_VISIBILITY_PRESET "hidden")
+
+# Broken LTO on GCC 4
+if (CMAKE_COMPILER_IS_GNUCXX AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 5)
+  set(BROKEN_LTO ON)
+endif ()
+
+if (NOT BROKEN_LTO AND CMAKE_VERSION VERSION_GREATER "3.8")
+  # CMake 3.9+
+  include(CheckIPOSupported)
+  check_ipo_supported(RESULT HAVE_IPO)
+  if (HAVE_IPO)
+    set(CMAKE_INTERPROCEDURAL_OPTIMIZATION TRUE)
+  endif ()
+endif ()
+
+add_subdirectory(../.. fmt)
+set_property(TARGET fmt PROPERTY POSITION_INDEPENDENT_CODE ON)
+
+add_library(library-test SHARED library.cc)
+target_link_libraries(library-test PRIVATE fmt::fmt)
+
+add_executable(exe-test main.cc)
+target_link_libraries(exe-test PRIVATE library-test)

vendor/Fmt/test/static-export-test/library.cc

@@ -0,0 +1,5 @@
+#include <fmt/compile.h>
+
+__attribute__((visibility("default"))) std::string foo() {
+  return fmt::format(FMT_COMPILE("foo bar {}"), 4242);
+}

vendor/Fmt/test/static-export-test/main.cc

@@ -0,0 +1,6 @@
+#include <iostream>
+#include <string>
+
+extern std::string foo();
+
+int main() { std::cout << foo() << std::endl; }