Fix build

Declare a HOST_PTHREAD_LINKFLAGS variable to hold the flags
required to link with pthreads, and use it for the solver addon.

Works on GNU/Linux, please test and fix for other platforms.

build/jam/BuildSetup

@@ -427,6 +427,7 @@ if $(HOST_PLATFORM_BEOS_COMPATIBLE) {
 	HOST_LIBBE = libbe_build.so ;
 	HOST_ADD_BUILD_COMPATIBILITY_LIB_DIR
 		= "export LIBRARY_PATH=$LIBRARY_PATH:$(HOST_BUILD_COMPATIBILITY_LIB_DIR)" ;
+	HOST_PTHREAD_LINKFLAGS = ;
 	HOST_LIBRARY_NAME_MAP_input_server = /system/servers/input_server ;
 	HOST_DEFINES += __STDC_FORMAT_MACROS __STDC_LIMIT_MACROS ;
 
@@ -454,6 +455,15 @@ if $(HOST_PLATFORM_BEOS_COMPATIBLE) {
 			= "export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:$(HOST_BUILD_COMPATIBILITY_LIB_DIR)" ;
 	}
 
+	if $(HOST_PLATFORM) = cygwin {
+		# not needed
+		HOST_PTHREAD_LINKFLAGS = ;
+	} else if $(HOST_PLATFORM) = freebsd {
+		HOST_PTHREAD_LINKFLAGS = -pthread ;
+	} else {
+		HOST_PTHREAD_LINKFLAGS = -pthread ;
+	}
+
 	# the C++ support library
 	if $(HOST_GCC_VERSION[1]) < 3 {
 		HOST_LIBSUPC++ = ;

src/build/libpackage/solver/Jamfile

@@ -15,6 +15,8 @@ SEARCH_SOURCE += [ FDirName $(HAIKU_TOP) src kits package solver ] ;
 MakeLocate libpackage-add-on-libsolv_build.so
 	: $(HOST_BUILD_COMPATIBILITY_LIB_DIR) ;
 
+LINKFLAGS on libpackage-add-on-libsolv_build.so += $(HOST_PTHREAD_LINKFLAGS) ;
+
 BuildPlatformSharedLibrary libpackage-add-on-libsolv_build.so
 	:
 	LibsolvSolver.cpp