IA MCU is based on Intel Pentium ISA without x87 and passing parameters
in registers.  We want to optimize for IA MCU without changing existing
Pentium codegen.  This patch adds PROCESSOR_IAMCU for -march=iamcu,
which is based on -march=pentium with updated cost tables.

gcc/

	PR target/66749
	* config/i386/i386.c (iamcu_cost): New.
	(m_IAMCU): Likewise.
	(initial_ix86_arch_features): Disable X86_ARCH_CMOV for m_IAMCU.
	(processor_target_table): Add an entry for "iamcu".
	(processor_alias_table): Likewise.
	(ix86_issue_rate): Handle PROCESSOR_IAMCU.
	(ix86_adjust_cost): Likewise.
	(ia32_multipass_dfa_lookahead): Likewise.
	* config/i386/i386.h (processor_type): Add PROCESSOR_IAMCU.
	* config/i386/x86-tune.def: Updated for m_IAMCU.

gcc/testsuite/

	PR target/66749
	* gcc.target/i386/pr66749.c: New test.

From-SVN: r225460