[testsuite][arm] Update warning prune regex

r269586 changed the format of some warning messages.

Each switch in the warning message is now surrounded by single quotes.

This commit updates the regex's in arm.exp dejagnu files to match the
new format and remove the extra 20+ FAILs on excess errors that are
introduced on certain variations (e.g.
arm-eabi-aem/-marm/-march=armv7-a/-mfpu=vfpv3-d16/-mfloat-abi=softfp).

Regtested arm.exp with cross-compiler arm-none-eabi

gcc/testsuite/ChangeLog:

2019-04-12  Matthew Malcomson  <matthew.malcomson@arm.com>

	* g++.target/arm/arm.exp: Change format of default prune regex.
	* gcc.target/arm/arm.exp: Change format of default prune regex.

From-SVN: r270316

gcc/testsuite/ChangeLog

+2019-04-12  Matthew Malcomson  <matthew.malcomson@arm.com>
+
+	* g++.target/arm/arm.exp: Change format of default prune regex.
+	* gcc.target/arm/arm.exp: Change format of default prune regex.
+
 2019-04-12  Martin Liska  <mliska@suse.cz>
 
 	PR middle-end/89970

gcc/testsuite/g++.target/arm/arm.exp

@@ -35,7 +35,7 @@ if ![info exists DEFAULT_CXXFLAGS] then {
 
 global dg_runtest_extra_prunes
 set dg_runtest_extra_prunes ""
-lappend dg_runtest_extra_prunes "warning: switch -m(cpu|arch)=.* conflicts with -m(cpu|arch)=.* switch"
+lappend dg_runtest_extra_prunes "warning: switch '-m(cpu|arch)=.*' conflicts with '-m(cpu|arch)=.*' switch"
 
 # Initialize `dg'.
 dg-init

gcc/testsuite/gcc.target/arm/arm.exp

@@ -33,7 +33,7 @@ if ![info exists DEFAULT_CFLAGS] then {
 # This variable should only apply to tests called in this exp file.
 global dg_runtest_extra_prunes
 set dg_runtest_extra_prunes ""
-lappend dg_runtest_extra_prunes "warning: switch -m(cpu|arch)=.* conflicts with -m(cpu|arch)=.* switch"
+lappend dg_runtest_extra_prunes "warning: switch '-m(cpu|arch)=.*' conflicts with '-m(cpu|arch)=.*' switch"
 
 # Initialize `dg'.
 dg-init