x86emul: suppress "not built" warning for test harness'es run targets

The run* targets can be used to test whatever the tool chain is capable
of building, as long as at least the main harness source file builds.
Don't probe the tools chain, in particular to avoid issuing the warning,
in this case. While looking into this I also noticed the wording of the
respective comment isn't quite right, which therefore gets altered at
the same time.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

tools/tests/x86_emulator/Makefile

@@ -97,11 +97,13 @@ avx512dq-opmask-vecs := 1 2
 avx512bw-opmask-vecs := 4 8
 
 # Suppress building by default of the harness if the compiler can't deal
-# with any of the extensions used.  Don't alter the "run" target dependencies
+# with some of the extensions used.  Don't alter the "run" target dependencies
 # though, as this target needs to be specified manually, and things may work
 # partially even with older compilers.
 TARGET-y := $(TARGET)
 
+ifeq ($(filter run%,$(MAKECMDGOALS)),)
+
 define simd-check-cc
 TARGET-$(shell echo 'int i;' | $(CC) -x c -c -o /dev/null -m$(1) - || echo y) :=
 endef
@@ -116,6 +118,8 @@ ifeq ($(TARGET-y),)
 $(warning Test harness not built, use newer compiler than "$(CC)" (version $(shell $(CC) -dumpversion)) and an "{evex}" capable assembler)
 endif
 
+endif
+
 all: $(TARGET-y)
 
 # For AVX and later, have the compiler avoid XMM0 to widen coverage of