iscsi: link libm into the module

Depending on the configuration of QEMU, some binaries might not need libm
at all.  In that case libiscsi, which uses exp(), will fail to load.
Link it in the module explicitly.

Reported-by: Yi Sun <yisun@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/meson.build b/meson.build
index a45f1a8..913cf2a 100644
--- a/meson.build
+++ b/meson.build
@@ -163,7 +163,7 @@
 endif
 multiprocess_allowed = targetos == 'linux' and not get_option('multiprocess').disabled()
 
-m = cc.find_library('m', required: false)
+libm = cc.find_library('m', required: false)
 util = cc.find_library('util', required: false)
 winmm = []
 socket = []
@@ -1899,7 +1899,7 @@
 util_ss = util_ss.apply(config_all, strict: false)
 libqemuutil = static_library('qemuutil',
                              sources: util_ss.sources() + stub_ss.sources() + genh,
-                             dependencies: [util_ss.dependencies(), m, glib, socket, malloc, pixman])
+                             dependencies: [util_ss.dependencies(), libm, glib, socket, malloc, pixman])
 qemuutil = declare_dependency(link_with: libqemuutil,
                               sources: genh + version_res)