intel/tools: add missing include for stdarg.h

intel/tools: add missing include for stdarg.h

Fixes build in GCC 8.1.1:

FAILED: src/intel/tools/src@intel@tools@@intel_dump_gpu@sha/aub_write.c.o
gcc -Isrc/intel/tools/src@intel@tools@@intel_dump_gpu@sha -Isrc/intel/tools -I../../src/intel/tools -Isrc/../include -I../../src/../include -Isrc -I../../src -Isrc/mapi -I../../src/mapi -Isrc/mesa -I../../src/mesa -I../../src/gallium/include -I../../src/gallium/auxiliary -Isrc/intel -I../../src/intel -I../../include/drm-uapi -fdiagnostics-color=always -pipe -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -std=c99 -O2 -g -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS '-DVERSION="18.2.0-devel"' -DPACKAGE_VERSION=VERSION '-DPACKAGE_BUGREPORT="https://bugs.freedesktop.org/enter_bug.cgi?product=Mesa"' -DGLX_USE_TLS -DENABLE_ST_OMX_BELLAGIO=0 -DENABLE_ST_OMX_TIZONIA=0 -DHAVE_X11_PLATFORM -DGLX_INDIRECT_RENDERING -DGLX_DIRECT_RENDERING -DGLX_USE_DRM -DHAVE_DRM_PLATFORM -DHAVE_SURFACELESS_PLATFORM -DENABLE_SHADER_CACHE -DHAVE___BUILTIN_BSWAP32 -DHAVE___BUILTIN_BSWAP64 -DHAVE___BUILTIN_CLZ -DHAVE___BUILTIN_CLZLL -DHAVE___BUILTIN_CTZ -DHAVE___BUILTIN_EXPECT -DHAVE___BUILTIN_FFS -DHAVE___BUILTIN_FFSLL -DHAVE___BUILTIN_POPCOUNT -DHAVE___BUILTIN_POPCOUNTLL -DHAVE___BUILTIN_UNREACHABLE -DHAVE_FUNC_ATTRIBUTE_CONST -DHAVE_FUNC_ATTRIBUTE_FLATTEN -DHAVE_FUNC_ATTRIBUTE_MALLOC -DHAVE_FUNC_ATTRIBUTE_PURE -DHAVE_FUNC_ATTRIBUTE_UNUSED -DHAVE_FUNC_ATTRIBUTE_WARN_UNUSED_RESULT -DHAVE_FUNC_ATTRIBUTE_WEAK -DHAVE_FUNC_ATTRIBUTE_FORMAT -DHAVE_FUNC_ATTRIBUTE_PACKED -DHAVE_FUNC_ATTRIBUTE_RETURNS_NONNULL -DHAVE_FUNC_ATTRIBUTE_VISIBILITY -DHAVE_FUNC_ATTRIBUTE_ALIAS -DHAVE_FUNC_ATTRIBUTE_NORETURN -D_GNU_SOURCE -DUSE_SSE41 -DUSE_GCC_ATOMIC_BUILTINS -DUSE_X86_64_ASM -DMAJOR_IN_SYSMACROS -DHAVE_SYS_SYSCTL_H -DHAVE_LINUX_FUTEX_H -DHAVE_ENDIAN_H -DHAVE_STRTOF -DHAVE_MKOSTEMP -DHAVE_POSIX_MEMALIGN -DHAVE_TIMESPEC_GET -DHAVE_MEMFD_CREATE -DHAVE_STRTOD_L -DHAVE_DLADDR -DHAVE_DL_ITERATE_PHDR -DHAVE_ZLIB -DHAVE_PTHREAD -DHAVE_LIBDRM -DHAVE_LLVM=0x0600 -DMESA_LLVM_VERSION_PATCH=1 -DHAVE_VALGRIND -DHAVE_LIBUNWIND -DHAVE_WAYLAND_PLATFORM -DWL_HIDE_DEPRECATED -DHAVE_DRI3 -DHAVE_DRI3_MODIFIERS -Wall -Werror=implicit-function-declaration -Werror=missing-prototypes -fno-math-errno -fno-trapping-math -Wno-missing-field-initializers -fPIC -fvisibility=hidden -Wno-override-init  -MD -MQ 'src/intel/tools/src@intel@tools@@intel_dump_gpu@sha/aub_write.c.o' -MF 'src/intel/tools/src@intel@tools@@intel_dump_gpu@sha/aub_write.c.o.d' -o 'src/intel/tools/src@intel@tools@@intel_dump_gpu@sha/aub_write.c.o' -c ../../src/intel/tools/aub_write.c
../../src/intel/tools/aub_write.c: In function ‘fail_if’:
../../src/intel/tools/aub_write.c:243:4: error: implicit declaration of function ‘va_start’; did you mean ‘assert’? [-Werror=implicit-function-declaration]
    va_start(args, format);
    ^~~~~~~~
    assert
../../src/intel/tools/aub_write.c:245:4: error: implicit declaration of function ‘va_end’; did you mean ‘rand’? [-Werror=implicit-function-declaration]
    va_end(args);
    ^~~~~~
    rand
cc1: some warnings being treated as errors

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>