The leading - makes it rather inconsistent with the majority of other
projects around the world. Use the form everyone else uses.
To solve this, properly pass prefix to inner makes as was always
intended.
Fixes: https://github.com/libopencm3/libopencm3/issues/1058
Renamed every instance of variable CFLAGS in target specific Makefiles
to TGT_CFLAGS to free up CFLAGS for user defined compiler flags.
Added information in README.md about existence and usage of CFLAGS
environment variable in build process.
-ggdb3 make slightly bigger .elf files, but allows gdb to understand
macros, which libopenocm3 uses somewhat extensively. Make this the
default, and pull it up to the common base makefile, so it can be easily
substituted.
On linux, the output of CP rule was try to write to / which is - of course, forbidden for write.
This solution adds to each part of lib correct pointer to the root of lib where the libs should be written.
Bug found by Kuldeep Singh Dhaka.
