libplacebo-1.21.0 fails to build with glslang-7.13.3496 due to header move

[...]
[26/50] x86_64-pc-linux-gnu-c++ -Isrc/25a6634@@placebo@sha -Isrc -I../libplacebo-1.21.0/src -I../libplacebo-1.21.0/src/./include -I../libplacebo-1.21.0/subprojects/xtalloc/include -I../libplacebo-1.21.0/subprojects/bstr/include -fdiagnostics-color=always -pipe -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Wnon-virtual-dtor -g -Wall -Wundef -Wshadow -Wparentheses -Wpointer-arith -std=c++11 -fvisibility=hidden -march=native -O2 -march=native -O2 -fPIC -pthread -MD -MQ 'src/25a6634@@placebo@sha/glsl_glslang.cc.o' -MF 'src/25a6634@@placebo@sha/glsl_glslang.cc.o.d' -o 'src/25a6634@@placebo@sha/glsl_glslang.cc.o' -c ../libplacebo-1.21.0/src/glsl/glslang.cc
FAILED: src/25a6634@@placebo@sha/glsl_glslang.cc.o 
x86_64-pc-linux-gnu-c++ -Isrc/25a6634@@placebo@sha -Isrc -I../libplacebo-1.21.0/src -I../libplacebo-1.21.0/src/./include -I../libplacebo-1.21.0/subprojects/xtalloc/include -I../libplacebo-1.21.0/subprojects/bstr/include -fdiagnostics-color=always -pipe -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Wnon-virtual-dtor -g -Wall -Wundef -Wshadow -Wparentheses -Wpointer-arith -std=c++11 -fvisibility=hidden -march=native -O2 -march=native -O2 -fPIC -pthread -MD -MQ 'src/25a6634@@placebo@sha/glsl_glslang.cc.o' -MF 'src/25a6634@@placebo@sha/glsl_glslang.cc.o.d' -o 'src/25a6634@@placebo@sha/glsl_glslang.cc.o' -c ../libplacebo-1.21.0/src/glsl/glslang.cc
../libplacebo-1.21.0/src/glsl/glslang.cc:28:10: fatal error: SPIRV/GlslangToSpv.h: No such file or directory
   28 | #include <SPIRV/GlslangToSpv.h>
      |          ^~~~~~~~~~~~~~~~~~~~~~
compilation terminated.
ninja: build stopped: subcommand failed.
[...]

https://github.com/KhronosGroup/glslang/commit/7b0e236325fa9e8ebc7f446f83797a20a2263b70 moved headers to a glslang subdirectory which appeared in the latest glslang release 7.13.3496. I've reported the problem here: https://github.com/KhronosGroup/glslang/issues/1959 but it looks like upstream wants its users to go along with that change.