[libgomp, testsuite] Fix insufficient resources in test-cases

When running libgomp test-case broadcast-many.c on an nvptx accelerator
(T400, driver version 470.86), I run into:
...
libgomp: The Nvidia accelerator has insufficient resources to launch \
  'main$_omp_fn$0' with num_workers = 32 and vector_length = 32; \
  recompile the program with 'num_workers = x and vector_length = y' on \
  that offloaded region or '-fopenacc-dim=:x:y' where x * y <= 896.

FAIL: libgomp.oacc-c/../libgomp.oacc-c-c++-common/broadcast-many.c \
  -DACC_DEVICE_TYPE_nvidia=1 -DACC_MEM_SHARED=0 -foffload=nvptx-none  \
  -O0  execution test
...

The error does not occur when using GOMP_NVPTX_JIT=-O0.

Fix this by using 896 / 32 == 28 workers for ACC_DEVICE_TYPE_nvidia.

Likewise for some other test-cases.

Tested libgomp on x86_64 with nvptx accelerator.

libgomp/ChangeLog:

2022-01-27  Tom de Vries  <tdevries@suse.de>

	* testsuite/libgomp.oacc-c-c++-common/broadcast-many.c: Reduce
	num_workers for nvidia accelerator to fix libgomp error 'insufficient
	resources'.
	* testsuite/libgomp.oacc-c-c++-common/par-loop-comb-reduction-4.c:
	Same.
	* testsuite/libgomp.oacc-c-c++-common/reduction-7.c: Same.

libgomp/testsuite/libgomp.oacc-c-c++-common/broadcast-many.c

@@ -5,6 +5,13 @@
 #include <assert.h>
 #include <stdio.h>
 
+#if ACC_DEVICE_TYPE_nvidia
+/* To avoid 'libgomp: The Nvidia accelerator has insufficient resources'.  */
+#define NUM_WORKERS 28
+#else
+#define NUM_WORKERS 32
+#endif
+
 #define LOCAL(n) double n = input;
 #define LOCALS(n) LOCAL(n##1) LOCAL(n##2) LOCAL(n##3) LOCAL(n##4) \
 		  LOCAL(n##5) LOCAL(n##6) LOCAL(n##7) LOCAL(n##8)
@@ -23,7 +30,7 @@ int main (void)
   int ret;
   int input = 1;
 
-  #pragma acc parallel num_gangs(1) num_workers(32) copyout(ret)
+  #pragma acc parallel num_gangs(1) num_workers(NUM_WORKERS) copyout(ret)
   {
     int w = 0;
     LOCALS2(h);

libgomp/testsuite/libgomp.oacc-c-c++-common/par-loop-comb-reduction-4.c

@@ -1,5 +1,12 @@
 #include <assert.h>
 
+#if ACC_DEVICE_TYPE_nvidia
+/* To avoid 'libgomp: The Nvidia accelerator has insufficient resources'.  */
+#define NUM_WORKERS 24
+#else
+#define NUM_WORKERS 32
+#endif
+
 /* Test of reduction on both parallel and loop directives (workers and vectors
    together in gang-partitioned mode, float type, multiple reductions).  */
 
@@ -13,7 +20,8 @@ main (int argc, char *argv[])
   for (i = 0; i < 32768; i++)
     arr[i] = i % (32768 / 64);
 
-  #pragma acc parallel num_gangs(32) num_workers(32) vector_length(32) \
+  #pragma acc parallel \
+    num_gangs(32) num_workers(NUM_WORKERS) vector_length(32) \
     reduction(+:res) reduction(max:mres) copy(res, mres)
   {
     #pragma acc loop gang /* { dg-warning "nested loop in reduction needs reduction clause for 'm\?res'" "TODO" } */

libgomp/testsuite/libgomp.oacc-c-c++-common/reduction-7.c

@@ -181,6 +181,12 @@ void gwv_np_3()
   assert (res == hres);
 }
 
+#if ACC_DEVICE_TYPE_nvidia
+/* To avoid 'libgomp: The Nvidia accelerator has insufficient resources'.  */
+#define NUM_WORKERS 28
+#else
+#define NUM_WORKERS 32
+#endif
 
 /* Test of reduction on loop directive (gangs, workers and vectors, multiple
    non-private reduction variables, float type).  */
@@ -194,7 +200,7 @@ void gwv_np_4()
   for (i = 0; i < 32768; i++)
     arr[i] = i % (32768 / 64);
 
-  #pragma acc parallel num_gangs(32) num_workers(32) vector_length(32)
+  #pragma acc parallel num_gangs(32) num_workers(NUM_WORKERS) vector_length(32)
   {
     #pragma acc loop gang reduction(+:res) reduction(max:mres)
     for (j = 0; j < 32; j++)
@@ -235,6 +241,7 @@ void gwv_np_4()
   assert (mres == hmres);
 }
 
+#undef NUM_WORKERS
 
 /* Test of reduction on loop directive (vectors, private reduction
    variable).  */