After compiling mesa-git on commit 0661c357c60 from the AUR pkgbuild, I can now
confirm my system seems to have become impervious to the above "vega_crasher"
program.

Output from said program after resizing and moving vega_crasher's window a bit,
in case it was important:

L CALLBACK:  type = 0x8251, severity = 0x826b, message = LLVM diagnostic
(remark): <unknown>:0:0: 9 instructions in function
GL CALLBACK:  type = 0x8251, severity = 0x826b, message = Shader Stats: SGPRS:
16 VGPRS: 24 Code Size: 52 LDS: 0 Scratch: 0 Max Waves: 10 Spilled SGPRs: 0
Spilled VGPRs: 0 PrivMem VGPRs: 0
GL CALLBACK:  type = 0x8251, severity = 0x826b, message = LLVM diagnostic
(remark): <unknown>:0:0: 12 instructions in function
GL CALLBACK:  type = 0x8251, severity = 0x826b, message = Shader Stats: SGPRS:
16 VGPRS: 8 Code Size: 92 LDS: 0 Scratch: 0 Max Waves: 10 Spilled SGPRs: 0
Spilled VGPRs: 0 PrivMem VGPRs: 0
GL CALLBACK:  type = 0x8251, severity = 0x826b, message = Shader Stats: SGPRS:
16 VGPRS: 24 Code Size: 44 LDS: 0 Scratch: 0 Max Waves: 10 Spilled SGPRs: 0
Spilled VGPRs: 0 PrivMem VGPRs: 0
GL CALLBACK:  type = 0x8251, severity = 0x826b, message = Shader Stats: SGPRS:
16 VGPRS: 8 Code Size: 80 LDS: 0 Scratch: 0 Max Waves: 10 Spilled SGPRs: 0
Spilled VGPRs: 0 PrivMem VGPRs: 0
GL CALLBACK:  type = 0x8251, severity = 0x826b, message = LLVM diagnostic
(remark): <unknown>:0:0: 2 instructions in function
GL CALLBACK:  type = 0x8251, severity = 0x826b, message = LLVM diagnostic
(remark): <unknown>:0:0: 3 instructions in function
GL CALLBACK:  type = 0x8251, severity = 0x826b, message = LLVM diagnostic
(remark): <unknown>:0:0: 4 instructions in function
GL CALLBACK:  type = 0x8251, severity = 0x826b, message = Shader Stats: SGPRS:
16 VGPRS: 24 Code Size: 44 LDS: 0 Scratch: 0 Max Waves: 10 Spilled SGPRs: 0
Spilled VGPRs: 0 PrivMem VGPRs: 0
GL CALLBACK:  type = 0x8251, severity = 0x826b, message = Shader Stats: SGPRS:
16 VGPRS: 8 Code Size: 136 LDS: 0 Scratch: 0 Max Waves: 10 Spilled SGPRs: 0
Spilled VGPRs: 0 PrivMem VGPRs: 0
GL CALLBACK:  type = 0x8251, severity = 0x826b, message = LLVM diagnostic
(remark): <unknown>:0:0: 16 instructions in function
GL CALLBACK:  type = 0x8251, severity = 0x826b, message = Shader Stats: SGPRS:
24 VGPRS: 24 Code Size: 92 LDS: 0 Scratch: 0 Max Waves: 10 Spilled SGPRs: 0
Spilled VGPRs: 0 PrivMem VGPRs: 0
GL CALLBACK:  type = 0x8251, severity = 0x826b, message = Shader Stats: SGPRS:
24 VGPRS: 24 Code Size: 88 LDS: 0 Scratch: 0 Max Waves: 10 Spilled SGPRs: 0
Spilled VGPRs: 0 PrivMem VGPRs: 0

Minetest will take longer to test as the pkgbuild doesn't enable asserts, and
also because of adformentioned $dayjob. I guess in that case I'd only know if I
saw garbled output; it was never very consistent when it occured but would
always be during the loading bar screen (but when it did happen some very
colourful blocky corruption would result).