cmake: fix mingw-llvm shared linking

mingw-llvm can't handle the '--exclude-libs' linker flag, so
we'll have to skip it.

At the same time, cmake can't locate the boost shared libs as the
import libs are not generated when using mingw-llvm due to boost's
clang-linux.jam file. For now, we'll patch the cmake files, using
the dlls as import libs (which is allowed by mingw).

While at it, we'll avoid linking the static AND dynamic boost libs,
speeding the build.

Signed-off-by: Lucian Petrut <lpetrut@cloudbasesolutions.com>

src/CMakeLists.txt

@@ -814,7 +814,8 @@ if(WITH_LIBCEPHFS)
       OUTPUT_NAME cephfs
       VERSION 2.0.0
       SOVERSION 2)
-    if(NOT APPLE)
+    if(NOT APPLE AND NOT
+        (WIN32 AND CMAKE_CXX_COMPILER_ID STREQUAL Clang))
       foreach(name ceph-common client osdc)
         set_property(TARGET cephfs APPEND_STRING PROPERTY
           LINK_FLAGS " -Wl,--exclude-libs,lib${name}.a")

win32_build.sh

@@ -231,8 +231,12 @@ if [[ -z $SKIP_DLL_COPY ]]; then
         $lz4Dir/lib/dll/liblz4-1.dll
         $sslDir/bin/libcrypto-1_1-x64.dll
         $sslDir/bin/libssl-1_1-x64.dll
-        $mingwLibpthreadDir/libwinpthread-1.dll
-        $boostDir/lib/*.dll)
+        $mingwLibpthreadDir/libwinpthread-1.dll)
+    if [[ $ENABLE_SHARED == "ON" ]]; then
+        required_dlls+=(
+            $boostDir/lib/*.dll
+        )
+    fi
     if [[ -n $USE_MINGW_LLVM ]]; then
         required_dlls+=(
             $mingwTargetLibDir/libc++.dll

win32_deps_build.sh

@@ -6,6 +6,7 @@ SCRIPT_DIR="$(dirname "$BASH_SOURCE")"
 SCRIPT_DIR="$(realpath "$SCRIPT_DIR")"
 
 USE_MINGW_LLVM=${USE_MINGW_LLVM:-}
+ENABLE_SHARED=${ENABLE_SHARED:-OFF}
 
 num_vcpus=$(nproc)
 NUM_WORKERS=${NUM_WORKERS:-$num_vcpus}
@@ -236,15 +237,32 @@ EOL
 
 ./bootstrap.sh
 
+if [[ $ENABLE_SHARED == "ON" ]]; then
+    b2_link="shared"
+else
+    b2_link="static"
+fi
+
 ./b2 install --user-config=user-config.jam toolset=$b2toolset \
     target-os=windows release \
-    link=static,shared \
+    link=$b2_link \
     threadapi=win32 --prefix=$boostDir \
     address-model=64 architecture=x86 \
     binary-format=pe abi=ms -j $NUM_WORKERS \
     -sZLIB_INCLUDE=$zlibDir/include -sZLIB_LIBRARY_PATH=$zlibDir/lib \
     --without-python --without-mpi --without-log --without-wave
 
+if [[ -n $USE_MINGW_LLVM && $ENABLE_SHARED == "ON" ]]; then
+    # b2 doesn't generate import libs when using mingw-llvm. We'll tell cmake
+    # to use the dlls instead of import libs, which mingw is capable of.
+    #
+    # TODO: consider dropping this if we get to fix Boost's clang-linux.jam
+    # file. Worth mentioning that Boost might drop the import libs altogether:
+    # https://github.com/bfgroup/b2/issues/278
+    find $boostDir/lib/cmake -name "*.cmake" \
+        -exec sed -i 's/IMPORTED_LOCATION_RELEASE/IMPORTED_IMPLIB_RELEASE/g' {} \;
+fi
+
 echo "Building libbacktrace."
 cd $depsSrcDir
 if [[ ! -d $backtraceSrcDir ]]; then