math/libxsmm: fix build on non-amd64

On non-amd64, PLATFORM=1 needs to be passed to disable JIT.

Also, add a way to read TBR that does not depend on glibc.

math/libxsmm/Makefile

@@ -8,8 +8,6 @@ COMMENT=	Library for dense and sparse matrix operations and deep learning
 LICENSE=	BSD3CLAUSE
 LICENSE_FILE=	${WRKSRC}/LICENSE.md
 
-ONLY_FOR_ARCHS=		amd64
-ONLY_FOR_ARCHS_REASON=	relies on hard-coded x86 code, and is only supported on 64-bit
 
 BUILD_DEPENDS=	bash:shells/bash
 
@@ -27,6 +25,12 @@ TEST_TARGET=	tests
 
 BINARY_ALIAS=	python=${PYTHON_CMD}
 
+.include <bsd.port.options.mk>
+
+.if ${ARCH} != amd64
+MAKE_ARGS+=	PLATFORM=1
+.endif
+
 post-install: # https://github.com/hfp/libxsmm/issues/413
 	${RMDIR} ${STAGEDIR}${PREFIX}/share/modules
 

math/libxsmm/files/patch-src_libxsmm__timer.c

@@ -0,0 +1,25 @@
+--- src/libxsmm_timer.c.orig	2021-11-25 15:39:20 UTC
++++ src/libxsmm_timer.c
+@@ -24,7 +24,7 @@
+ # pragma offload_attribute(pop)
+ #endif
+ 
+-#if defined(__powerpc64__)
++#if defined(__powerpc64__) && defined(__GLIBC__)
+ # include <sys/platform/ppc.h>
+ #endif
+ 
+@@ -37,9 +37,13 @@
+ 
+ #if defined(LIBXSMM_TIMER_TSC)
+ # if defined(__powerpc64__)
++#  if defined(__GLIBC__)
+ #   define LIBXSMM_TIMER_RDTSC(CYCLE) { \
+       CYCLE = __ppc_get_timebase(); \
+     }
++#  else
++#   define LIBXSMM_TIMER_RDTSC(CYCLE) asm volatile("mfspr %%r3, 268": "=r" (CYCLE));
++#  endif
+ # elif ((defined(__GNUC__) || defined(LIBXSMM_INTEL_COMPILER) || defined(__PGI)) && (64 <= (LIBXSMM_BITS)))
+ #   define LIBXSMM_TIMER_RDTSC(CYCLE) { libxsmm_timer_tickint libxsmm_timer_rdtsc_hi_; \
+       __asm__ __volatile__ ("rdtsc" : "=a"(CYCLE), "=d"(libxsmm_timer_rdtsc_hi_)); \