Revise DXC help text: "(must be used with /Fo <file>)"

Description
Several of DXC's tool options, such as /Qstrip_debug have help text like this added to the end: "(must be used with /Fo <file>)"
However, these options do not technically require /Fo to be used for dxc. This text may be confusing, so perhaps it should be removed.
These options may not do much without /Fo, since they impact what's included in the output specified by /Fo, but it's not invalid.

I think the text was added in relation to container modification. When you load a shader container from file with /dumpbin these options only apply to the new container output specified by /Fo, not the original loaded container file. It might make sense to emit a warning in a case where the option does nothing because you aren't outputting a container, but this text in the option isn't necessary.

These are the affected options:

• -extractrootsignature - It probably makes sense to leave the text on this option, since the only scenario this is used for is the /dumpbin container modification scenario.
• -Qstrip_debug
• -Qstrip_priv
• -Qstrip_reflect
• -Qstrip_rootsignature

Additionally, the /Qstrip_debug option says "Strip debug information from 4_0+ shader bytecode", which was inherited directly from FXC. Since DXC never produced 4_0 or 5_0 bytecode (only 6_0+), this is odd. FXC had it because of differences in functionality between DX9 and DX10 shader targets. The "4_0+" should probably be removed for DXC.

https://github.com/microsoft/DirectXShaderCompiler/blob/130877392c263888ef06bab768856d3dab1f1c9a/include/dxc/Support/HLSLOptions.td#L495-L496

Environment

• DXC version: any
• Host Operating System: any

Start at include/dxc/Support/HLSLOptions.td around lines 495-496 and inspect the help text for the listed DXC options. Verify the current output for these options, then update the misleading /Fo wording and the 4_0+ reference where appropriate. Done means the help text accurately describes DXC behavior, while the extract-rootsignature wording is retained.