perf tools: Don't hardcode host include path for libslang

Hardcoding /usr/include/slang is fundamentally incompatible with cross
compilation and will lead to the inability for a cross-compiled
environment to properly detect whether slang is available or not.

If /usr/include/slang is necessary that is a distribution specific
knowledge that could be solved with either a standard pkg-config .pc
file (which slang has) or simply overriding CFLAGS accordingly, but the
default perf Makefile should be clean of all of that.

Signed-off-by: Florian Fainelli <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Alexey Budankov <[e-mail]>
Cc: [e-mail]
Cc: Jakub Kicinski <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Quentin Monnet <[e-mail]>
Cc: Stanislav Fomichev <[e-mail]>
Fixes: ef7b93a11904 ("perf report: Librarize the annotation code and use it in the newt browser")
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/build/feature/Makefile

···
 	$(BUILD) -laudit
 
 $(OUTPUT)test-libslang.bin:
-	$(BUILD) -I/usr/include/slang -lslang
+	$(BUILD) -lslang
 
 $(OUTPUT)test-libcrypto.bin:
 	$(BUILD) -lcrypto

tools/perf/Makefile.config

···
     NO_SLANG := 1
   else
     # Fedora has /usr/include/slang/slang.h, but ubuntu /usr/include/slang.h
-    CFLAGS += -I/usr/include/slang
     CFLAGS += -DHAVE_SLANG_SUPPORT
     EXTLIBS += -lslang
     $(call detected,CONFIG_SLANG)