maint: allow selecting compiler for ManyConfigTests

Instead of hardcoding the compiler as `cc`, let a CC environment
variable dictate which compiler to use.

For example, in macOS/arm64 where the GNU compiler is provided by
brew the following will allow using it instead of the system compiler
(which ALSO answers to `gcc` eventhough is `clang`)

  % CC=gcc-13 maint/ManyConfigTests

maint/ManyConfigTests

@@ -110,11 +110,12 @@ tmp=/tmp/pcre2testing
 
 CFLAGS="-g"
 OFLAGS="-O0"
+CC="${CC:=cc}"
 ISGCC=0
 
 # If the compiler is gcc, add a lot of warning switches.
 
-cc --version >/tmp/pcre2ccversion 2>/dev/null
+$CC --version >/tmp/pcre2ccversion 2>/dev/null
 if [ $? -eq 0 ] && grep GCC /tmp/pcre2ccversion >/dev/null; then
   ISGCC=1
   CFLAGS="$CFLAGS -Wall"

src/pcre2_jit_neon_inc.h

@@ -87,7 +87,7 @@ POSSIBILITY OF SUCH DAMAGE.
 #pragma GCC diagnostic ignored "-Wdeclaration-after-statement"
 #endif
 
-#if (defined(__GNUC__) && __SANITIZE_ADDRESS__) \
+#if (defined(__GNUC__) && defined(__SANITIZE_ADDRESS__) && __SANITIZE_ADDRESS__ ) \
 	|| (defined(__clang__) \
 	&& ((__clang_major__ == 3 && __clang_minor__ >= 3) || (__clang_major__ > 3)))
 __attribute__((no_sanitize_address))