No longer builds with -Dlibrsvg=disabled due to missing libm for exp()

[ionenwks]

Regression from https://github.com/eXeC64/imv/commit/8e46aa0238df85e7b9a2394066cc90c273cd5ae2

FAILED: imv-msg 
cc  -o imv-msg imv-msg.p/src_binds.c.o imv-msg.p/src_bitmap.c.o imv-msg.p/src_canvas.c.o imv-msg.p/src_commands.c.o imv-msg.p/src_console.c.o imv-msg.p/src_image.c.o imv-msg.p/src_imv.c.o imv-msg.p/src_ipc.c.o imv-msg.p/src_ipc_common.c.o imv-msg.p/src_keyboard.c.o imv-msg.p/src_list.c.o imv-msg.p/src_log.c.o imv-msg.p/src_navigator.c.o imv-msg.p/src_source.c.o imv-msg.p/src_viewport.c.o imv-msg.p/src_imv_msg.c.o imv-msg.p/src_dummy_window.c.o -Wl,--as-needed -Wl,--no-undefined -Wl,--start-group /usr/lib64/libpangocairo-1.0.so /usr/lib64/libpango-1.0.so /usr/lib64/libgobject-2.0.so /usr/lib64/libglib-2.0.so /usr/lib64/libharfbuzz.so /usr/lib64/libcairo.so /usr/lib64/libGL.so -pthread /usr/lib64/libxkbcommon.so /usr/lib64/libicuio.so /usr/lib64/libicui18n.so /usr/lib64/libicuuc.so /usr/lib64/libicudata.so /usr/lib64/libinih.so -lfreeimage /usr/lib64/libtiff.so /usr/lib64/libpng16.so /usr/lib64/libz.so /usr/lib64/libturbojpeg.so /usr/lib64/libnsgif.so /usr/lib64/libheif.so -Wl,--end-group
/usr/lib/gcc/x86_64-pc-linux-gnu/10.3.0/../../../../x86_64-pc-linux-gnu/bin/ld: imv-msg.p/src_viewport.c.o: undefined reference to symbol 'exp@@GLIBC_2.29'
/usr/lib/gcc/x86_64-pc-linux-gnu/10.3.0/../../../../x86_64-pc-linux-gnu/bin/ld: /lib64/libm.so.6: error adding symbols: DSO missing from command line
collect2: error: ld returned 1 exit status