nir: Fix lower_two_sided_color when the face is an input

Fixes the two-sided-lighting and vertex-program-two-side piglit tests
on Panfrost.

v2: Use an existing variable for gl_FrontFacing if present.

Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Rob Clark <robdclark@chromium.org>
Status Job ID Name Coverage
  Container+Docs
manual #3633760
aarch64 manual
arm_build
manual #3633761
manual
arm_test-base
manual #3633757
manual
x86_build-base
manual #3633759
manual
x86_build_old
manual #3633758
manual
x86_test-base
 
  Container 2
created #3633770
arm64_test
created #3633765
i386_build
created #3633762
aarch64
kernel+rootfs_arm64
created #3633763
aarch64
kernel+rootfs_armhf
created #3633766
ppc64el_build
created #3633767
s390x_build
created #3633764
x86_build
created #3633768
x86_test-gl
created #3633769
x86_test-vk
 
  Meson X86 64
created #3633774
meson-clang
created #3633773
meson-classic
created #3633775
meson-clover
created #3633776
meson-clover-old-llvm
created #3633772
meson-gallium
created #3633771
meson-testing
created #3633777
meson-vulkan
 
  Scons
created #3633778
allowed to fail
scons-win64
 
  Meson Misc
created #3633780
aarch64
meson-arm64
created #3633781
aarch64
meson-arm64-build-test
created #3633779
aarch64
meson-armhf
created #3633782
meson-i386
created #3633785
meson-mingw32-x86_64
created #3633784
kvm
meson-ppc64el
created #3633783
kvm
meson-s390x
 
  Llvmpipe
created #3633789
llvmpipe-gles2
created #3633790
llvmpipe-traces
created #3633787
piglit-glslparser
created #3633786
piglit-quick_gl
created #3633788
piglit-quick_shader
 
  Softpipe
created #3633791
softpipe-gles2
created #3633794
softpipe-gles31 1/4
created #3633792
softpipe-gles3 1/2
created #3633795
softpipe-gles31 2/4
created #3633796
softpipe-gles31 3/4
created #3633797
softpipe-gles31 4/4
created #3633793
softpipe-gles3 2/2
 
  Freedreno
created #3633802
google-freedreno-db410c
arm64_a306_gles2
created #3633803
google-freedreno-db410c
arm64_a306_gles3
created #3633804
google-freedreno-db410c
arm64_a306_gles3_options
created #3633805
google-freedreno-db820c
arm64_a530_gles2
created #3633806
google-freedreno-db820c
arm64_a530_gles3
created #3633807
google-freedreno-db820c
arm64_a530_gles31
created #3633798
google-freedreno-cheza
arm64_a630_gles2
created #3633800
google-freedreno-cheza
arm64_a630_gles3
created #3633799
google-freedreno-cheza
arm64_a630_gles31
created #3633801
google-freedreno-cheza
arm64_a630_vk
 
  Panfrost
created #3633808
mesa-ci-aarch64-lava-collabora
panfrost-t720-gles2:arm64
created #3633809
mesa-ci-aarch64-lava-collabora
panfrost-t760-gles2:armhf
created #3633810
mesa-ci-aarch64-lava-collabora
panfrost-t860-gles2:arm64
created #3633811
mesa-ci-aarch64-lava-collabora
panfrost-t860-gles3:arm64
 
  Radv
created #3633812
radv-fossils
 
  Virgl
created #3633820
virgl-gl30-on-gl
created #3633821
virgl-gl31-on-gl
created #3633822
virgl-gl32-on-gl
created #3633813
virgl-gles2-on-gl
created #3633816
virgl-gles31-on-gl 1/4
created #3633817
virgl-gles31-on-gl 2/4
created #3633818
virgl-gles31-on-gl 3/4
created #3633819
virgl-gles31-on-gl 4/4
created #3633814
virgl-gles3-on-gl 1/2
created #3633815
virgl-gles3-on-gl 2/2
created #3633823
virgl-traces