[CMake] libta-lib.so does not link against `libm` causing missing math symbols at runtime

[BwL1289]

When building TA-Lib using the CMake build system, the produced shared library (libta-lib.so) is not linked against libm, resulting in multiple undefined math symbols at runtime and is only linked against libc:

[./lib/libta-lib.so.0.6.4]:
    linux-vdso.so.1 (0x0000ffff98a32000)
    libc.so.6 => /lib64/libc.so.6 (0x0000ffff986fe000)
    /lib/ld-linux-aarch64.so.1 (0x0000ffff989e5000)
undefined symbol: atan	(./lib/libta-lib.so.0.6.4)
undefined symbol: sin	(./lib/libta-lib.so.0.6.4)
undefined symbol: cos	(./lib/libta-lib.so.0.6.4)
undefined symbol: sqrt	(./lib/libta-lib.so.0.6.4)
undefined symbol: acos	(./lib/libta-lib.so.0.6.4)
undefined symbol: asin	(./lib/libta-lib.so.0.6.4)
undefined symbol: log10	(./lib/libta-lib.so.0.6.4)
undefined symbol: tan	(./lib/libta-lib.so.0.6.4)
undefined symbol: sinh	(./lib/libta-lib.so.0.6.4)
undefined symbol: exp	(./lib/libta-lib.so.0.6.4)
undefined symbol: cosh	(./lib/libta-lib.so.0.6.4)
undefined symbol: log	(./lib/libta-lib.so.0.6.4)
undefined symbol: tanh	(./lib/libta-lib.so.0.6.4)

This does not occur when building using the Autotools (configure) build, which correctly links -lm build here.

The CMake build includes checks for the existence of math-related functions here however, it never links libm into the shared library, except in a special-case used only for tests here. This linking step never happens for the actual build target (ta_lib or ta-lib), leading to missing symbols in the final shared library.

The fix should be something like:

target_link_libraries(ta_lib PRIVATE m)

For example, here's how OpenBLAS does it.