tools build: Add new build support

Adding new build framework into 'tools/build' to be used by tools.

There's no change for actual building at this point, it comes in the
next patches.

The idea and more details are explained in the
'tools/build/Documentation/Build.txt' file.

I adopted everything from the kernel build system, with some changes to
allow for multiple binaries build definitions.

While the kernel's build output is single image (forget modules) we need
to be able to build several binaries/libraries.

The basic idea is that sser provides 'Build' files with objects
definitions like:

  perf-y += a.o
  perf-y += b.o
  libperf-y += c.o
  libperf-y += d.o

and the build framework outputs files:

  perf-in.o    # a.o, b.o compiled in
  libperf-in.o # c.o, d.o compiled in

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Tested-by: Will Deacon <will.deacon@arm.com>
Cc: Alexis Berlemont <alexis.berlemont@gmail.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-fbj22h4av0otlxupwcmrxgpa@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/build/tests/ex/Build

@@ -0,0 +1,8 @@
+ex-y += ex.o
+ex-y += a.o
+ex-y += b.o
+ex-y += empty/
+
+libex-y += c.o
+libex-y += d.o
+libex-y += arch/

tools/build/tests/ex/Makefile

@@ -0,0 +1,23 @@
+export srctree := ../../../..
+export CC      := gcc
+export LD      := ld
+export AR      := ar
+
+build := -f $(srctree)/tools/build/Makefile.build dir=. obj
+ex: ex-in.o libex-in.o
+	gcc -o $@ $^
+
+ex.%: FORCE
+	make -f $(srctree)/tools/build/Makefile.build dir=. $@
+
+ex-in.o: FORCE
+	make $(build)=ex
+
+libex-in.o: FORCE
+	make $(build)=libex
+
+clean:
+	find . -name '*.o' -delete -o -name '\.*.cmd' -delete -o -name '\.*.d' -delete
+	rm -f ex ex.i ex.s
+
+.PHONY: FORCE

tools/build/tests/ex/a.c

@@ -0,0 +1,5 @@
+
+int a(void)
+{
+	return 0;
+}

tools/build/tests/ex/arch/Build

@@ -0,0 +1,2 @@
+libex-y += e.o
+libex-y += f.o

tools/build/tests/ex/arch/e.c

@@ -0,0 +1,5 @@
+
+int e(void)
+{
+	return 0;
+}

tools/build/tests/ex/arch/f.c

@@ -0,0 +1,5 @@
+
+int f(void)
+{
+	return 0;
+}

tools/build/tests/ex/b.c

@@ -0,0 +1,5 @@
+
+int b(void)
+{
+	return 0;
+}

tools/build/tests/ex/c.c

@@ -0,0 +1,5 @@
+
+int c(void)
+{
+	return 0;
+}

tools/build/tests/ex/d.c

@@ -0,0 +1,5 @@
+
+int d(void)
+{
+	return 0;
+}

tools/build/tests/ex/ex.c

@@ -0,0 +1,19 @@
+
+int a(void);
+int b(void);
+int c(void);
+int d(void);
+int e(void);
+int f(void);
+
+int main(void)
+{
+	a();
+	b();
+	c();
+	d();
+	e();
+	f();
+
+	return 0;
+}