*-symbols-check: error out when using unset variables

It will make bugs like the one fixed with previous patch dead obvious.

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>

amdgpu/amdgpu-symbol-check

@@ -1,5 +1,7 @@
 #!/bin/bash
 
+set -u
+
 # The following symbols (past the first five) are taken from the public headers.
 # A list of the latter should be available Makefile.am/libdrm_amdgpuinclude_HEADERS
 

etnaviv/etnaviv-symbol-check

@@ -1,5 +1,7 @@
 #!/bin/bash
 
+set -u
+
 # The following symbols (past the first five) are taken from the public headers.
 # A list of the latter should be available Makefile.sources/LIBDRM_ETNAVIV_H_FILES
 

exynos/exynos-symbol-check

@@ -1,5 +1,7 @@
 #!/bin/bash
 
+set -u
+
 # The following symbols (past the first five) are taken from the public headers.
 # A list of the latter should be available Makefile.am/libdrm_exynos*_HEADERS
 

freedreno/freedreno-symbol-check

@@ -1,5 +1,7 @@
 #!/bin/bash
 
+set -u
+
 # The following symbols (past the first five) are taken from the public headers.
 # A list of the latter should be available Makefile.sources/LIBDRM_FREEDRENO_H_FILES
 

intel/intel-symbol-check

@@ -1,5 +1,7 @@
 #!/bin/bash
 
+set -u
+
 # The following symbols (past the first five) are taken from the public headers.
 # A list of the latter should be available Makefile.sources/LIBDRM_INTEL_H_FILES
 

libkms/kms-symbol-check

@@ -1,5 +1,7 @@
 #!/bin/bash
 
+set -u
+
 # The following symbols (past the first five) are taken from the public headers.
 # A list of the latter should be available Makefile.sources/LIBKMS_H_FILES
 

nouveau/nouveau-symbol-check

@@ -1,5 +1,7 @@
 #!/bin/bash
 
+set -u
+
 # The following symbols (past the first five) are taken from the public headers.
 # A list of the latter should be available Makefile.sources/LIBDRM_NOUVEAU_H_FILES
 

omap/omap-symbol-check

@@ -1,5 +1,7 @@
 #!/bin/bash
 
+set -u
+
 # The following symbols (past the first five) are taken from the public headers.
 # A list of the latter should be available Makefile.am/libdrm_omap*HEADERS
 

radeon/radeon-symbol-check

@@ -1,5 +1,7 @@
 #!/bin/bash
 
+set -u
+
 # The following symbols (past the first five) are taken from the public headers.
 # A list of the latter should be available Makefile.sources/LIBDRM_RADEON_H_FILES
 

tegra/tegra-symbol-check

@@ -1,5 +1,7 @@
 #!/bin/bash
 
+set -u
+
 # The following symbols (past the first nine) are taken from tegra.h.
 
 FUNCS=$($NM -D --format=bsd --defined-only ${1-.libs/libdrm_tegra.so} | awk '{print $3}'| while read func; do