CMake: fix msys/ICU compilation failure

Author: 0xFFFC0000

CMakeLists.txt

@@ -1115,7 +1115,19 @@ if(MINGW)
   if(DEPENDS)
     set(ICU_LIBRARIES icuio icui18n icuuc icudata icutu iconv)
   else()
-    set(ICU_LIBRARIES icuio icuin icuuc icudt icutu iconv)
+    # This is an extremely ugly hack to get around Boost not being built with static ICU.
+    # We reported the issue, we are waiting for upstream to fix this issue: https://github.com/boostorg/boost/issues/1079#issue-3384962885
+    # This hack links shared ICU libs to avoid linker errors we get in MSYS2 compilation (undefined symbols to ICU).
+    set(OLD_LIB_SUFFIXES ${CMAKE_FIND_LIBRARY_SUFFIXES})
+    set(CMAKE_FIND_LIBRARY_SUFFIXES ".dll.a")
+    find_library(ICUIO_LIBRARIES NAMES icuio REQUIRED)
+    find_library(ICUIN_LIBRARIES NAMES icuin REQUIRED)
+    find_library(ICUUC_LIBRARIES NAMES icuuc REQUIRED)
+    find_library(ICUDT_LIBRARIES NAMES icudt REQUIRED)
+    find_library(ICUTU_LIBRARIES NAMES icutu REQUIRED)
+    find_library(ICONV_LIBRARIES NAMES iconv REQUIRED)
+    set(ICU_LIBRARIES ${ICUIO_LIBRARIES} ${ICUIN_LIBRARIES} ${ICUUC_LIBRARIES} ${ICUDT_LIBRARIES} ${ICUTU_LIBRARIES} ${ICONV_LIBRARIES})
+    set(CMAKE_FIND_LIBRARY_SUFFIXES ${OLD_LIB_SUFFIXES})
   endif()
 elseif(APPLE OR OPENBSD OR ANDROID)
   set(EXTRA_LIBRARIES "")