PCH: Add genex support for REUSE_FROM signature

Fixes: #20523
20 jobs for !5766 with pch-reuse-from-genex in 8 minutes and 14 seconds (queued for 2 seconds)
latest detached
Status Job ID Name Coverage
  Build
manual #5531288
linux docker build cmake manual
build:centos6-x86_64
passed #5531285
linux docker build cmake
build:debian10-iwyu

00:05:42

manual #5531289
linux-3.17 linux docker build cmake manual
build:fedora33-ninja
passed #5531287
linux-3.17 linux docker build cmake
build:fedora33-sphinx

00:04:20

passed #5531286
linux-3.17 linux docker build cmake
build:fedora33-tidy

00:08:13

manual #5531291
nonconcurrent xcode-12.3 shell macos cmake manual
build:macos-makefiles
manual #5531290
nonconcurrent xcode-12.3 shell macos cmake manual
build:macos-ninja
manual #5531292
nonconcurrent msvc-19.28 vs2019 shell windows cmake manual
build:windows-vs2019-x64-ninja
 
  Test
created #5531293
x11 linux-3.17 linux docker cmake
test:fedora33-ninja
created #5531295
nonconcurrent xcode-12.3 shell macos cmake
test:macos-makefiles
created #5531294
nonconcurrent xcode-12.3 shell macos cmake
test:macos-ninja
created #5531296
nonconcurrent msvc-19.28 vs2019 shell windows cmake
test:windows-vs2019-x64-ninja
 
  Test Ext
created #5531299
linux docker cuda-rt cmake
test:cuda10.2-nvidia
created #5531297
linux-3.17 linux docker build cmake
test:debian10-ninja
created #5531298
linux-3.17 linux docker build cmake
test:fedora33-makefiles
created #5531300
linux-3.17 linux docker build cmake
test:fedora33-ninja-multi
created #5531301
concurrent xcode-12.3 shell macos cmake
test:macos-xcode
created #5531302
concurrent msvc-19.28 vs2019 shell windows cmake
test:windows-vs2019-x64
 
  External
passed cdash

passed ghostflow-check-master