perf map: Tighten snprintf() string precision to pass gcc check on some 32-bit arches

Noticed on a debian:experimental mips and mipsel cross build build
environment:

  perfbuilder@ec265a086e9b:~$ mips-linux-gnu-gcc --version | head -1
  mips-linux-gnu-gcc (Debian 10.2.1-3) 10.2.1 20201224
  perfbuilder@ec265a086e9b:~$

    CC       /tmp/build/perf/util/map.o
  util/map.c: In function 'map__new':
  util/map.c:109:5: error: '%s' directive output may be truncated writing between 1 and 2147483645 bytes into a region of size 4096 [-Werror=format-truncation=]
    109 |    "%s/platforms/%s/arch-%s/usr/lib/%s",
        |     ^~
  In file included from /usr/mips-linux-gnu/include/stdio.h:867,
                   from util/symbol.h:11,
                   from util/map.c:2:
  /usr/mips-linux-gnu/include/bits/stdio2.h:67:10: note: '__builtin___snprintf_chk' output 32 or more bytes (assuming 4294967321) into a destination of size 4096
     67 |   return __builtin___snprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1,
        |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     68 |        __bos (__s), __fmt, __va_arg_pack ());
        |        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  cc1: all warnings being treated as errors

Since we have the lenghts for what lands in that place, use it to give
the compiler more info and make it happy.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/util/map.c b/tools/perf/util/map.c
index 692e56d..fbc40a2 100644
--- a/tools/perf/util/map.c
+++ b/tools/perf/util/map.c
@@ -77,8 +77,7 @@
 	if (strstarts(filename, "/system/lib/")) {
 		char *ndk, *app;
 		const char *arch;
-		size_t ndk_length;
-		size_t app_length;
+		int ndk_length, app_length;
 
 		ndk = getenv("NDK_ROOT");
 		app = getenv("APP_PLATFORM");
@@ -106,8 +105,8 @@
 		if (new_length > PATH_MAX)
 			return false;
 		snprintf(newfilename, new_length,
-			"%s/platforms/%s/arch-%s/usr/lib/%s",
-			ndk, app, arch, libname);
+			"%.*s/platforms/%.*s/arch-%s/usr/lib/%s",
+			ndk_length, ndk, app_length, app, arch, libname);
 
 		return true;
 	}