It helps to understand Bug 1693208 .

Backed out for causing cpp bustage on RenderTextureHostSWGL.cpp

backout: https://hg.mozilla.org/integration/autoland/rev/0b213a6414cd679a927ecd3b4a5dd1b6160f684c

push: https://treeherder.mozilla.org/jobs?repo=autoland&selectedTaskRun=YHebLiZMTSicCq1PaQkZ6w.0&revision=11b157c81a3afc21dd2bc43d7ff55d4152f7da32&searchStr=Linux%2Cx64%2Copt%2CC%2FC%2B%2B%2Cchecks%2Csource-test-clang-non-unified%2Cnon-unified

failure log: https://treeherder.mozilla.org/logviewer?job_id=330203553&repo=autoland&lineNumber=7846

[task 2021-02-17T07:43:58.458Z] 41:30.50 /builds/worker/fetches/clang/bin/clang++ -std=gnu++17 -o /dev/null -c -I/builds/worker/checkouts/gecko/obj-x86_64-pc-linux-gnu/dist/stl_wrappers -I/builds/worker/checkouts/gecko/obj-x86_64-pc-linux-gnu/dist/system_wrappers -include /builds/worker/checkouts/gecko/config/gcc_hidden.h -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 -fstack-protector-strong -fstack-clash-protection -ftrivial-auto-var-init=pattern -DDEBUG=1 -DOS_POSIX=1 -DOS_LINUX=1 -DMOZ_HAS_MOZGLUE -DMOZILLA_INTERNAL_API [..] /builds/worker/checkouts/gecko/gfx/webrender_bindings/RendererOGL.cpp -fsyntax-only
[task 2021-02-17T07:43:58.710Z] /builds/worker/checkouts/gecko/gfx/webrender_bindings/RenderTextureHostSWGL.cpp:173:7: error: use of undeclared identifier 'gfxCriticalNote'; did you mean 'gfx_critical_note'?
[task 2021-02-17T07:43:58.710Z] gfxCriticalNote << "Unhandled external image format: " << GetFormat();
[task 2021-02-17T07:43:58.710Z] ^~~~~~~~~~~~~~~
[task 2021-02-17T07:43:58.710Z] gfx_critical_note
[task 2021-02-17T07:43:58.711Z] /builds/worker/checkouts/gecko/obj-x86_64-pc-linux-gnu/dist/include/mozilla/webrender/webrender_ffi_generated.h:3379:13: note: 'gfx_critical_note' declared here
[task 2021-02-17T07:43:58.711Z] extern void gfx_critical_note(const char *aMsg);
[task 2021-02-17T07:43:58.711Z] ^
[task 2021-02-17T07:43:58.711Z] /builds/worker/checkouts/gecko/gfx/webrender_bindings/RenderTextureHostSWGL.cpp:173:23: error: invalid operands to binary expression ('void (const char *)' and 'const char [34]')
[task 2021-02-17T07:43:58.711Z] gfxCriticalNote << "Unhandled external image format: " << GetFormat();
[task 2021-02-17T07:43:58.711Z] ~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[task 2021-02-17T07:43:58.862Z] 2 errors generated.

Updated fix addressed the build failure.
https://treeherder.mozilla.org/jobs?repo=try&revision=cc18564dc01b8a8a2ca4e524386810b9f7ceed58

https://hg.mozilla.org/mozilla-central/rev/528cb2116f20