perf build: Error if jevents won't work and NO_JEVENTS=1 isn't set

Rather than disabling jevents if a sufficient python isn't present
error in the build. This avoids the build progressing but the binary
being degraded. The build can still succeed by specifying NO_JEVENTS=1
to the build and this is conveyed in the error message.

Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andres Freund <andres@anarazel.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Martin Liška <mliska@suse.cz>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Pavithra Gurushankar <gpavithrasha@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Quentin Monnet <quentin@isovalent.com>
Cc: Roberto Sassu <roberto.sassu@huawei.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: Tiezhu Yang <yangtiezhu@loongson.cn>
Cc: Tom Rix <trix@redhat.com>
Cc: Yang Jihong <yangjihong1@huawei.com>
Cc: llvm@lists.linux.dev
Link: https://lore.kernel.org/r/20230311065753.3012826-2-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Makefile.config

@@ -880,14 +880,12 @@ endif
 ifneq ($(NO_JEVENTS),1)
   NO_JEVENTS := 0
   ifndef PYTHON
-    $(warning No python interpreter disabling jevent generation)
-    NO_JEVENTS := 1
+    $(error ERROR: No python interpreter needed for jevents generation. Install python or build with NO_JEVENTS=1.)
   else
     # jevents.py uses f-strings present in Python 3.6 released in Dec. 2016.
     JEVENTS_PYTHON_GOOD := $(shell $(PYTHON) -c 'import sys;print("1" if(sys.version_info.major >= 3 and sys.version_info.minor >= 6) else "0")' 2> /dev/null)
     ifneq ($(JEVENTS_PYTHON_GOOD), 1)
-      $(warning Python interpreter too old (older than 3.6) disabling jevent generation)
-      NO_JEVENTS := 1
+      $(error ERROR: Python interpreter needed for jevents generation too old (older than 3.6). Install a newer python or build with NO_JEVENTS=1.)
     endif
   endif
 endif