testsuite: Sanitize pacbti test cases for Cortex-M

testsuite: Sanitize pacbti test cases for Cortex-M

Some of the test cases were scanning for "bti", but it would,
incorrectly, match the ".arch_extenssion pacbti".

gcc/testsuite/ChangeLog:

	* gcc.target/arm/bti-1.c: Check for asm instructions starting
	with a tab.
	* gcc.target/arm/bti-2.c: Likewise.
	* gcc.target/arm/pac-1.c: Likewise.
	* gcc.target/arm/pac-2.c: Likewise.
	* gcc.target/arm/pac-3.c: Likewise.
	* gcc.target/arm/pac-4.c: Likewise.
	* gcc.target/arm/pac-6.c: Likewise.
	* gcc.target/arm/pac-7.c: Likewise.
	* gcc.target/arm/pac-8.c: Likewise.
	* gcc.target/arm/pac-9.c: Likewise.
	* gcc.target/arm/pac-10.c: Likewise.
	* gcc.target/arm/pac-11.c: Likewise.
	* gcc.target/arm/pac-15.c: Likewise.
	* gcc.target/arm/pac-sibcall.c: Likewise.

Signed-off-by: Torbjörn SVENSSON <torbjorn.svensson@foss.st.com>
Co-authored-by: Yvan ROUX <yvan.roux@foss.st.com>