testsuite: Adjust cpp2a/lambda-uneval regrex

testsuite: Adjust cpp2a/lambda-uneval regrex

Both lambda-uneval1.C and lambda-uneval5.C test that a symbol is not
declared global by looking for "globl" assembler directive.  The testcases
generate the "lglobl" directive in AIX XCOFF, which is a false positive.
This patch restricts the regex to ignore a prepended "l".  The patch
also tightens the regex to specifically look for space, tab or period
between the "globl" and the symbol.

Tested on powerpc-ibm-aix7.2.3.0 and powerpc64le-linux-gnu.

	* g++.dg/cpp2a/lambda-uneval1.C: Ignore preceding "l" and
	intervening period.
	* g++.dg/cpp2a/lambda-uneval5.C: Ignore preceding "l" and
	explicitly check for intervening space, tab or period.