#6 Fix parallel Make issue with slibtool + other issues

[orbea]

This is a patch applied against ta-lib-0.4.0 that fixes a few build issues.

1. Renames configure.in to configure.ac as is standard.
2. Adds detection to configure.ac for libm to replaced the hardcoded instances of -lm.
3. Links internal dependencies with .la files rather than -l linker flags. The -l linker flags are for external dependencies exclusively and this can break with slibtool.
4. With slibtool there is a parellel make issue where gen_code binary is copied to ../../../bin before it is created and the Makefile.am needs to explicitly list gen_code as a prerequisite for the 'all-local' target. This probably happens because slibtool is significantly faster than GNU libtool.
5. Additionally slibtool will output the gen_code binary to the .libs directory while slibtool will do so in the Makefile directory. The command needs to be invoked with $(LIBTOOL) --mode=execute to correctly copy the binary and not the slibtool wrapper script for the binary.
6. Lastly there is a workaround for a slibtool bug where the cp(1) command is wrapped in a shell script. Invoking the command directly with --mode=execute will result in slibtool dropping the destination argument which obviously does not work. While this workaround is far from ideal, it will be portable for GNU libtool, slibtool now and slibtool when the bug is fixed.

Gentoo Bug: https://bugs.gentoo.org/790770