Backport #27594 by @sryze
1. `make build` fails because `||` and `&&` have the same precedence in
sh/bash, so the `false` command always evaluated (leading to an error).
```
+ which gmake /usr/local/bin/gmake
+ false
*** Failed target: .BEGIN
*** Failed command: which "gmake" || printf "Error: GNU Make is
required!\n\n" 1>&2 && false
*** Error code 1
```
2. When `GPREFIX` is set to an empty string with quotation marks,
`gmake` mistakenly thinks that it's a file name:
``` gmake: *** empty string invalid as file name. Stop. ```
Co-authored-by: Sergey Zolotarev <sryze@protonmail.com>
The syntax of the gitea Makefile is not platform-agnostic and is
specific to the GNU version of `make`. BSD platforms such as FreeBSD
ship with bmake (BSD make) as their default `make` program; attempting
to compile gitea by simply executing `make` causes a wall of errors to
show as a result of syntax incompatible with BSD make.
If a file named `BSDmakefile` is present, `bmake` will give it
preference over a generic `Makefile`. This `BSDmakefile` is taken from
the BSD-licensed `gmake-proxy` project [0], which transparently proxies
all `make` commands to `gmake` (GNU make) on systems where `bmake` is
the default, and if `gmake` is not installed an error message is
displayed.
[0]: https://github.com/neosmart/gmake-proxy
