Alpha/testsuite: Run target testing over all the usual optimization levels

Use `gcc-dg-runtest' test driver rather than `dg-runtest' to run the
Alpha testsuite as several targets already do.  Add `-Og -g' and `-Oz'
as well via ADDITIONAL_TORTURE_OPTIONS to expand coverage.  Adjust test
options across individual test cases accordingly where required.

Discard base-2.c, cix-2.c, and max-2.c test cases as they merely are
optimization variants of base-1.c, cix-1.c, and max-1.c respectively,
run at `-O2' rather than the default level (`-O0'), now covered by the
framework with the latter ones in a generic way.

Old test results:

		=== gcc Summary ===

# of expected passes		44

vs new ones:
		=== gcc Summary ===

# of expected passes		364
# of unsupported tests		5

	gcc/testsuite/
	* gcc.target/alpha/alpha.exp: Use `gcc-dg-runtest' rather than
	`dg-runtest'.  Add `-Og -g' and `-Oz' variants via
	ADDITIONAL_TORTURE_OPTIONS.
	* gcc.target/alpha/20000715-1.c: Adjust test options
	accordingly.
	* gcc.target/alpha/20011018-1.c: Likewise.
	* gcc.target/alpha/980217-1.c: Likewise.
	* gcc.target/alpha/asm-1.c: Likewise.
	* gcc.target/alpha/pr105209.c: Likewise.
	* gcc.target/alpha/pr106966.c: Likewise.
	* gcc.target/alpha/pr115297.c: Likewise.
	* gcc.target/alpha/pr115526.c: Likewise.
	* gcc.target/alpha/pr19518.c: Likewise.
	* gcc.target/alpha/pr22093.c: Likewise.
	* gcc.target/alpha/pr24178.c: Likewise.
	* gcc.target/alpha/pr39740.c: Likewise.
	* gcc.target/alpha/pr42113.c: Likewise.
	* gcc.target/alpha/pr42269-1.c: Likewise.
	* gcc.target/alpha/pr42448-1.c: Likewise.
	* gcc.target/alpha/pr42448-2.c: Likewise.
	* gcc.target/alpha/pr42774.c: Likewise.
	* gcc.target/alpha/pr61586.c: Likewise.
	* gcc.target/alpha/pr66140.c: Likewise.
	* gcc.target/alpha/pr83628-1.c: Likewise.
	* gcc.target/alpha/pr83628-2.c: Likewise.
	* gcc.target/alpha/pr83628-3.c: Likewise.
	* gcc.target/alpha/pr86984.c: Likewise.
	* gcc.target/alpha/sqrt.c: Likewise.
	* gcc.target/alpha/base-2.c: Remove file.
	* gcc.target/alpha/cix-2.c: Remove file.
	* gcc.target/alpha/max-2.c: Remove file.