meta: 32 bit linux is experimental

PR-URL: #16723
Refs: nodejs/build#885
Refs: nodejs/nodejs.org#1446
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>

BUILDING.md

@@ -39,7 +39,7 @@ in production.
 
 |  System      | Support type | Version                          | Architectures        | Notes            |
 |--------------|--------------|----------------------------------|----------------------|------------------|
-| GNU/Linux    | Tier 1       | kernel >= 2.6.32, glibc >= 2.12  | x86, x64, arm, arm64 |                  |
+| GNU/Linux    | Tier 1       | kernel >= 2.6.32, glibc >= 2.12  | x64, arm, arm64      |                  |
 | macOS        | Tier 1       | >= 10.10                         | x64                  |                  |
 | Windows      | Tier 1       | >= Windows 7 / 2008 R2           | x86, x64             | vs2017           |
 | SmartOS      | Tier 2       | >= 15 < 16.4                     | x86, x64             | see note1        |
@@ -48,6 +48,7 @@ in production.
 | AIX          | Tier 2       | >= 7.1 TL04                      | ppc64be >=power7     |                  |
 | GNU/Linux    | Tier 2       | kernel >= 3.10, glibc >= 2.17    | s390x                |                  |
 | macOS        | Experimental | >= 10.8 < 10.10                  | x64                  | no test coverage |
+| GNU/Linux    | Experimental | kernel >= 2.6.32, glibc >= 2.12  | x86                  | limited CI       |
 | Linux (musl) | Experimental | musl >= 1.0                      | x64                  |                  |
 
 note1 - The gcc4.8-libs package needs to be installed, because node