by precompiling qgis.h
Needs to be precompiled for each target due to different includes, defines, etc. (~ 4 second for each target to build the precompiled header in below timings)
Executive summary:
- ~ 33% faster builds on ubuntu 22.04, QT5
- ~ 23% faster builds (only measured on qgis_core) on fedora:rawhide, QT6
- build artifact increase size: + ~7%
- shared library increase size: + 1% at most
Setup: laptop with Intel(R) Core(TM) i7-10750H CPU @ 2.60GHz, host OS Ubuntu 20.04,
QGIS built in Docker
Details:
* ubuntu 22.04, QT5, regular, CMAKE_BUILD_TYPE=Debug
```bash
$ time make -j12 qgis_core
real 9m8.566s
user 90m24.917s
sys 9m51.179s
$ du -c src/core | tail -n 1
1994796 total
$ ll ./output/lib/libqgis_core.so.3.41.0
-rwxr-xr-x 1 root root 590223936 Nov 30 00:35 ./output/lib/libqgis_core.so.3.41.0*
```
```bash
$ time make -j12 qgis_gui
real 8m26.430s
user 80m28.457s
sys 11m27.936s
$ du -c src/gui | tail -n 1
1538440 total
$ ll ./output/lib/libqgis_gui.so.3.41.0
-rwxr-xr-x 1 root root 454560448 Nov 30 00:47 ./output/lib/libqgis_gui.so.3.41.0*
```
```bash
$ time make -j12 qgis_app
real 4m55.189s
user 47m4.876s
sys 6m54.868s
$ du -c src/app | tail -n 1
783256 total
$ ll ./output/lib/libqgis_app.so.3.41.0
-rwxr-xr-x 1 root root 232041152 Nov 30 01:25 ./output/lib/libqgis_app.so.3.41.0*
```
* ubuntu 22.04, QT5, qgis.h as precompiled header, CMAKE_BUILD_TYPE=Debug:
```bash
$ time make -j12 qgis_core
real 6m3.472s
user 59m3.835s
sys 5m22.424s
$ du -c src/core | tail -n 1
2137448 total
$ ll ./output/lib/libqgis_core.so.3.41.0
-rwxr-xr-x 1 root root 598395456 Nov 30 00:56 ./output/lib/libqgis_core.so.3.41.0*
```
```bash
$ time make -j12 qgis_gui
real 5m45.719s
user 53m30.107s
sys 6m11.246s
$ du -c src/gui | tail -n 1
1660444 total
$ ll ./output/lib/libqgis_gui.so.3.41.0
-rwxr-xr-x 1 root root 456432320 Nov 30 01:04 ./output/lib/libqgis_gui.so.3.41.0*
```
```bash
$ time make -j12 qgis_analysis
real 2m36.504s
user 26m25.310s
sys 2m17.601s
$ du -c src/analysis/ | tail -n 1
920912 total
$ ll ./output/lib/libqgis_analysis.so.3.41.0
-rwxr-xr-x 1 root root 228178496 Nov 30 01:11 ./output/lib/libqgis_analysis.so.3.41.0*
```
```bash
$ time make -j12 qgis_3d
real 0m43.710s
user 6m9.148s
sys 0m39.859s
$ du -c src/3d | tail -n 1
315212 total
$ ll ./output/lib/libqgis_3d.so.3.41.0
-rwxr-xr-x 1 root root 58472960 Nov 30 01:14 ./output/lib/libqgis_3d.so.3.41.0*
```
```bash
$ time make -j12 qgis_app
real 3m35.156s
user 34m17.371s
sys 3m52.111s
$ du -c src/app | tail -n 1
905160 total
$ ll ./output/lib/libqgis_app.so.3.41.0
-rwxr-xr-x 1 root root 232577728 Nov 30 01:19 ./output/lib/libqgis_app.so.3.41.0*
```
* fedora:rawhide, QT6, regular, CMAKE_BUILD_TYPE=Debug:
```bash
$ time ninja qgis_core
real 13m47.521s
user 134m48.546s
sys 10m2.176s
$ du -c src/core | tail -n 1
2862200 total
$ ll ./output/lib/libqgis_core.so.3.41.0
-rwxr-xr-x 1 root root 824605072 Nov 30 00:53 ./output/lib/libqgis_core.so.3.41.0
```
* fedora:rawhide, QT6, qgis.h as precompiled header, CMAKE_BUILD_TYPE=Debug:
```bash
$ time ninja qgis_core
real 10m35.657s
user 97m51.161s
sys 7m59.564s
$ du -c src/core | tail -n 1
3028420 total
$ ll ./output/lib/libqgis_core.so.3.41.0
-rwxr-xr-x 1 root root 825732184 Nov 30 00:38 ./output/lib/libqgis_core.so.3.41.0
```
