gcc: link $lib/lib -> $lib/$targetConfig correctly and consistently

[ghost]

Description of changes

When native-compiling, gcc will install libraries into:

$lib/lib

When cross-compiling, gcc will install libraries into:

$lib/$targetConfig

When cross-compiling, we intended to create a link from $lib/lib to $lib/$targetConfig, so that downstream users can always safely assume that ${lib.getLib stdenv.cc.cc}/lib is where the gcc libraries are, regardless of whether stdenv.cc.cc is a cross compiler or a native compiler.

Unfortunately, there are two mistakes in how these links are created. Both of the mistakes are my fault:

1. The link would be created only when enableLibGccOutput==true

2. The link was being created from the incorrect source $lib/lib/lib instead of $lib/lib.

This commit corrects these mistakes by creating the link using ln -Ts (which is more predictable) and by putting the code which creates the link in gcc/common/builder.nix rather than in gcc/common/libgcc.nix.

CC: @trofi

Things done

• Building
  • x86_64-linux
  • powerpc64le-linux
  • aarch64-linux (cross from x86_64-linux)
  • mips64el-linux (cross from x86_64-linux)
  • tests.cross.sanity
• Fits CONTRIBUTING.md.

[ConnorBaker]

When I built the cross-compiler via

$ nom build .#pkgsCross.aarch64-multiplatform.stdenv.cc.cc.lib

I see that there's a nested lib directory so the libraries are in lib/lib -- is this intentional?

$ ls -la result-lib/lib/lib
total 8808
dr-xr-xr-x   2 root root    4096 Jan  1  1970 .
dr-xr-xr-x   3 root root    4096 Jan  1  1970 ..
-r-xr-xr-x   2 root root    1208 Jan  1  1970 libasan.la
lrwxrwxrwx 199 root root      16 Jan  1  1970 libasan.so -> libasan.so.8.0.0
lrwxrwxrwx 199 root root      16 Jan  1  1970 libasan.so.8 -> libasan.so.8.0.0
-r-xr-xr-x   2 root root 1678448 Jan  1  1970 libasan.so.8.0.0
-r-xr-xr-x   2 root root    1068 Jan  1  1970 libatomic.la
lrwxrwxrwx 289 root root      18 Jan  1  1970 libatomic.so -> libatomic.so.1.2.0
lrwxrwxrwx 289 root root      18 Jan  1  1970 libatomic.so.1 -> libatomic.so.1.2.0
-r-xr-xr-x   2 root root   90944 Jan  1  1970 libatomic.so.1.2.0
-r--r--r-- 175 root root     132 Jan  1  1970 libgcc_s.so
-r--r--r--   2 root root  150664 Jan  1  1970 libgcc_s.so.1
-r-xr-xr-x   2 root root    1050 Jan  1  1970 libgomp.la
lrwxrwxrwx 289 root root      16 Jan  1  1970 libgomp.so -> libgomp.so.1.0.0
lrwxrwxrwx 289 root root      16 Jan  1  1970 libgomp.so.1 -> libgomp.so.1.0.0
-r-xr-xr-x   2 root root  384936 Jan  1  1970 libgomp.so.1.0.0
-r-xr-xr-x   2 root root    1222 Jan  1  1970 libhwasan.la
lrwxrwxrwx  59 root root      18 Jan  1  1970 libhwasan.so -> libhwasan.so.0.0.0
lrwxrwxrwx  59 root root      18 Jan  1  1970 libhwasan.so.0 -> libhwasan.so.0.0.0
-r-xr-xr-x   2 root root  604896 Jan  1  1970 libhwasan.so.0.0.0
-r-xr-xr-x   2 root root    1038 Jan  1  1970 libitm.la
lrwxrwxrwx 289 root root      15 Jan  1  1970 libitm.so -> libitm.so.1.0.0
lrwxrwxrwx 289 root root      15 Jan  1  1970 libitm.so.1 -> libitm.so.1.0.0
-r-xr-xr-x   2 root root  183008 Jan  1  1970 libitm.so.1.0.0
-r-xr-xr-x   2 root root    1208 Jan  1  1970 liblsan.la
lrwxrwxrwx 257 root root      16 Jan  1  1970 liblsan.so -> liblsan.so.0.0.0
lrwxrwxrwx 257 root root      16 Jan  1  1970 liblsan.so.0 -> liblsan.so.0.0.0
-r-xr-xr-x   2 root root  604224 Jan  1  1970 liblsan.so.0.0.0
-r-xr-xr-x   2 root root    1038 Jan  1  1970 libssp.la
-r-xr-xr-x   2 root root    1020 Jan  1  1970 libssp_nonshared.la
lrwxrwxrwx 289 root root      15 Jan  1  1970 libssp.so -> libssp.so.0.0.0
lrwxrwxrwx 289 root root      15 Jan  1  1970 libssp.so.0 -> libssp.so.0.0.0
-r-xr-xr-x   2 root root   71440 Jan  1  1970 libssp.so.0.0.0
-r-xr-xr-x   2 root root    1008 Jan  1  1970 libstdc++exp.la
-r-xr-xr-x   2 root root    1005 Jan  1  1970 libstdc++fs.la
-r-xr-xr-x   2 root root    1065 Jan  1  1970 libstdc++.la
lrwxrwxrwx  11 root root      19 Jan  1  1970 libstdc++.so -> libstdc++.so.6.0.32
lrwxrwxrwx  11 root root      19 Jan  1  1970 libstdc++.so.6 -> libstdc++.so.6.0.32
-r-xr-xr-x   2 root root 3131784 Jan  1  1970 libstdc++.so.6.0.32
-r--r--r--   2 root root    2572 Jan  1  1970 libstdc++.so.6.0.32-gdb.py
-r-xr-xr-x   2 root root     999 Jan  1  1970 libsupc++.la
-r-xr-xr-x   2 root root    1208 Jan  1  1970 libtsan.la
lrwxrwxrwx 167 root root      16 Jan  1  1970 libtsan.so -> libtsan.so.2.0.0
lrwxrwxrwx 167 root root      16 Jan  1  1970 libtsan.so.2 -> libtsan.so.2.0.0
-r-xr-xr-x   2 root root 1495968 Jan  1  1970 libtsan.so.2.0.0
-r-xr-xr-x   2 root root    1215 Jan  1  1970 libubsan.la
lrwxrwxrwx 283 root root      17 Jan  1  1970 libubsan.so -> libubsan.so.1.0.0
lrwxrwxrwx 283 root root      17 Jan  1  1970 libubsan.so.1 -> libubsan.so.1.0.0
-r-xr-xr-x   2 root root  530304 Jan  1  1970 libubsan.so.1.0.0

Question about nested lib directory

[sternenseemann]

Cross lib dir seems wrong indeed, can confirm.