Generate efficient code for rotation patterns.

 Generate efficient code for rotation patterns.

     This change adds code to recognize rotation idioms and generate efficient instructions for them.

     Two new operators are added: GT_ROL and GT_ROR.

     The patterns recognized:
     (x << c1) | (x >>> c2) => x rol c1
     (x >>> c1) | (x << c2) => x ror c2

     where c1 and c2  are constant and c1 + c2 == bitsize(x)

     (x << y) | (x >>> (N - y)) => x rol y
     (x >>> y) | (x << (N - y)) => x ror y

     where N == bitsize(x)

     (x << y & M1) | (x >>> (N - y) & M2) => x rol y
     (x >>> y & M1) | (x << (N - y) & M2) => x ror y

     where N == bitsize(x)
     M1 & (N - 1) == N - 1
     M2 & (N - 1) == N - 1

     For a simple benchmark with 4 rotation patterns in a tight loop
     time goes from 7.324 to 2.600 (2.8 speedup).

     Rotations found and optimized in mscorlib:
     System.Security.Cryptography.SHA256Managed::RotateRight
     System.Security.Cryptography.SHA384Managed::RotateRight
     System.Security.Cryptography.SHA512Managed::RotateRight
     System.Security.Cryptography.RIPEMD160Managed:MDTransform (320 instances!)
     System.Diagnostics.Tracing.EventSource.Sha1ForNonSecretPurposes::Rol1
     System.Diagnostics.Tracing.EventSource.Sha1ForNonSecretPurposes::Rol5
     System.Diagnostics.Tracing.EventSource.Sha1ForNonSecretPurposes::Rol30
     System.Diagnostics.Tracing.EventSource.Sha1ForNonSecretPurposes::Drain
     (9 instances of Sha1ForNonSecretPurposes::Rol* inlined)

     Closes #1619.