cmake: simplify try_run result comparisons (#950) (#952)

Instead of looking at `MATCHES 0` which runs a regex and returns a false
positive for any result such as `10`, check if they are equal to `0`.
Also quote `0` to avoid looking it up as a variable (which was left
behind prior to the fix to use `${RETURN_VAR}` in the `c_run` macro).

Co-authored-by: Ben Boeckel <mathstuf@users.noreply.github.com>

config/cmake/ConfigureChecks.cmake

@@ -151,7 +151,7 @@ if (NOT WINDOWS)
         OUTPUT_VARIABLE OUTPUT
     )
     if (TEST_DIRECT_VFD_WORKS_COMPILE)
-      if (TEST_DIRECT_VFD_WORKS_RUN MATCHES 0)
+      if (TEST_DIRECT_VFD_WORKS_RUN EQUAL "0")
         HDF_FUNCTION_TEST (HAVE_DIRECT)
         set (CMAKE_REQUIRED_DEFINITIONS "${CMAKE_REQUIRED_DEFINITIONS} -D_GNU_SOURCE")
         add_definitions ("-D_GNU_SOURCE")
@@ -261,8 +261,8 @@ macro (C_RUN FUNCTION_NAME SOURCE_CODE RETURN_VAR)
       message (VERBOSE "* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * ")
     endif ()
 
-    if (${COMPILE_RESULT_VAR})
-      if (${RUN_RESULT_VAR} MATCHES 0)
+    if (COMPILE_RESULT_VAR)
+      if (RUN_RESULT_VAR EQUAL "0")
         set (${RETURN_VAR} 1 CACHE INTERNAL "Have C function ${FUNCTION_NAME}")
         if (CMAKE_VERSION VERSION_GREATER_EQUAL "3.15.0")
           message (VERBOSE "Testing C ${FUNCTION_NAME} - OK")
@@ -320,7 +320,7 @@ message (STATUS "Testing maximum decimal precision for C - ${PROG_OUTPUT4}")
 list (GET PROG_OUTPUT4 0 H5_LDBL_DIG)
 list (GET PROG_OUTPUT4 1 H5_FLT128_DIG)
 
-if (${HDF_PREFIX}_SIZEOF___FLOAT128 EQUAL 0 OR FLT128_DIG EQUAL 0)
+if (${HDF_PREFIX}_SIZEOF___FLOAT128 EQUAL "0" OR FLT128_DIG EQUAL "0")
   set (${HDF_PREFIX}_HAVE_FLOAT128 0)
   set (${HDF_PREFIX}_SIZEOF___FLOAT128 0)
   set (_PAC_C_MAX_REAL_PRECISION ${H5_LDBL_DIG})
@@ -346,7 +346,7 @@ macro (H5ConversionTests TEST msg)
         OUTPUT_VARIABLE OUTPUT
     )
     if (${TEST}_COMPILE)
-      if (${TEST}_RUN MATCHES 0)
+      if (${TEST}_RUN EQUAL "0")
         set (${TEST} 1 CACHE INTERNAL ${msg})
         if (CMAKE_VERSION VERSION_GREATER_EQUAL "3.15.0")
           message (VERBOSE "${msg}... yes")