* [build.zig] Overridable definitions from config.h
The new Options field "config" holds a string the user can set in the
format "-Dflag_a=1 -Dflag_b=0 ..." to override the values set in
`config.h`.
The file is parsed and the default values are appended to the
compilation flags, if the user doesn't override them.
The user string is appended to the compilation flags.
The "-DEXTERNAL_CONFIG_FLAGS" is added to prevent "config.h" inclusion.
Note: a certain format is assumed for the formatting of config.h
Note: this commit references the closed issue #3516
* [build.zig] Only SUPPORT_* definitions are overridable
Lines from `config.h` which contains "SUPPORT" are added to compilation after being parsed:
- remove whitespace
- format to preprocessor option https://gcc.gnu.org/onlinedocs/gcc/Preprocessor-Options.html
The user supplied flags have priority over the ones read from the file.
NOTE: extension to commit 4da7f82e6f, the logic is simplified
because the SUPPORT flags only have binary values, which makes them easier to parse.
b2d48ff172