Fix broken -emit-spirv-via-glsl test option (#7091)

Fixes issue #6898

The -emit-spirv-via-glsl slang-test option has been broken for
some amount of time. Tests that were using it were operating as
if using -emit-spirv-directly, leading to many duplicated tests.

After fixing the test option, there were an number of errors that
appeared as a result.

This change fixes the broken test option and the resulting test
errors. Some of the test errors revealed some legitimate issues,
such as:

-The GLSL bitCount instrinsic only supports 32-bit integers and
 requires emulation for other bit widths.
-Emitting GLSL 8-bit and 16-bit glsl integer types did not emit
 the proper extension requirements
-Emitting GLSL and casting for 16-bit integers was missing a
 closing parenthesis.
-Missing profile for GL_EXT_shader_explicit_arithmetic_types
-Missing toType cases for UInt8/Int8 for the kIROp_BitCast case
 in tryEmitInstExprImpl.

1 files changed, 3 insertions, 2 deletions

diff --git a/tests/bugs/gh-4305.slang b/tests/bugs/gh-4305.slang
index dd09bda1e..29d61f787 100644
--- a/tests/bugs/gh-4305.slang
+++ b/tests/bugs/gh-4305.slang
@@ -32,9 +32,10 @@ layout(local_size_x = 2, local_size_y = 2, local_size_z = 1) in;
 [DerivativeGroupLinear]
 #endif // #ifdef QUAD
 [numthreads(2, 2, 1)]
-#endif //#ifndef MODIFIER
+#endif // #ifndef MODIFIER
+[shader("compute")]
 void computeMain()
 {
     //BUF:1
     outputBuffer[0] = t2D.Sample(samplerState, float2(0.5, 0.5));
-}
\ No newline at end of file
+}