[InstrProf] Add the skipprofile attribute

As discussed in [0], this diff adds the `skipprofile` attribute to
prevent the function from being profiled while allowing profiled
functions to be inlined into it. The `noprofile` attribute remains
unchanged.

The `noprofile` attribute is used for functions where it is
dangerous to add instrumentation to while the `skipprofile` attribute is
used to reduce code size or performance overhead.

[0] https://discourse.llvm.org/t/why-does-the-noprofile-attribute-restrict-inlining/64108

Reviewed By: phosek

Differential Revision: https://reviews.llvm.org/D130807

llvm/lib/Bitcode/Writer/BitcodeWriter.cpp

@@ -698,6 +698,8 @@ static uint64_t getAttrKindEncoding(Attribute::AttrKind Kind) {
     return bitc::ATTR_KIND_NOCF_CHECK;
   case Attribute::NoProfile:
     return bitc::ATTR_KIND_NO_PROFILE;
+  case Attribute::SkipProfile:
+    return bitc::ATTR_KIND_SKIP_PROFILE;
   case Attribute::NoUnwind:
     return bitc::ATTR_KIND_NO_UNWIND;
   case Attribute::NoSanitizeBounds: