meson/android/scons/gallium: always define LLVM_AVAILABLE one way or the other

With the usual benefits of `#if` instead of `#ifdef`; mostly the fact
that typos are now build failures instead of silently being ignored.

Signed-off-by: Eric Engestrom <eric@engestrom.ch>
41 jobs for !3863 with llvm_available-always-defined in 17 minutes and 2 seconds (queued for 7 seconds)
latest detached
Status Job ID Name Coverage
  Container
passed #1663086
aarch64
arm_build

00:00:19

passed #1663087
aarch64
arm_test

00:00:21

passed #1663083
x86_build

00:00:22

passed #1663085
x86_build_old

00:00:23

passed #1663084
x86_test-gl

00:00:22

 
  Build
passed #1663091
aarch64
meson-arm64

00:03:55

passed #1663090
aarch64
meson-armhf

00:03:03

passed #1663092
meson-clang

00:07:00

passed #1663095
meson-clover

00:06:11

passed #1663096
meson-clover-old-llvm

00:05:41

passed #1663098
meson-i386

00:01:55

passed #1663089
meson-main

00:05:49

passed #1663101
meson-mingw32-x86_64

00:04:46

passed #1663100
gstreamer
meson-ppc64el

00:04:15

passed #1663099
gstreamer
meson-s390x

00:03:58

passed #1663088
meson-testing

00:05:52

passed #1663097
meson-vulkan

00:04:40

passed #1663102
scons

00:05:26

passed #1663103
scons-old-llvm

00:02:00

passed #1663093
scons-swr

00:05:35

passed #1663094
scons-win64

00:06:20

 
  Test
passed #1663122
db410c
arm64_a306_gles2

00:06:29

passed #1663119
mesa-cheza
arm64_a630_gles2

00:04:26

passed #1663121
mesa-cheza
arm64_a630_gles3

00:06:37

passed #1663120
mesa-cheza
arm64_a630_gles31

00:04:20

passed #1663107
lava-meson-gxl-s905x-libretech-cc
lima-mali450-test:arm64

00:09:16

passed #1663104
lava-sun50i-h6-pine-h64
panfrost-t720-test:arm64

00:09:44

passed #1663105
lava-rk3288-veyron-jaq
panfrost-t760-test:armhf

00:05:24

passed #1663106
lava-rk3399-gru-kevin
panfrost-t860-test:arm64

00:10:50

passed #1663109
piglit-glslparser

00:02:44

passed #1663108
piglit-quick_gl

00:09:32

passed #1663163
piglit-quick_shader

00:06:08

passed #1663111
test-llvmpipe-gles2

00:02:49

passed #1663112
test-softpipe-gles2

00:01:35

passed #1663115
test-softpipe-gles31 1/4

00:02:51

passed #1663113
test-softpipe-gles3 1/2

00:04:56

passed #1663116
test-softpipe-gles31 2/4

00:03:06

passed #1663117
test-softpipe-gles31 3/4

00:04:55

passed #1663118
test-softpipe-gles31 4/4

00:02:13

passed #1663114
test-softpipe-gles3 2/2

00:05:13

failed #1663110
piglit-quick_shader

00:00:13