build: improve parsing of gfortran version (#47352)

Co-authored-by: Jameson Nash <vtjnash@gmail.com>

Make.inc

@@ -1140,8 +1140,11 @@ USE_BINARYBUILDER ?= 0
 endif
 
 # Auto-detect triplet once, create different versions that we use as defaults below for each BB install target
-FC_VERSION := $(shell $(FC) --version 2>/dev/null | head -1)
-FC_OR_CC_VERSION := $(or $(FC_VERSION),$(shell $(CC) --version 2>/dev/null | head -1))
+FC_VERSION := $(shell $(FC) -dM -E - < /dev/null | grep __GNUC__ | cut -d' ' -f3)
+ifeq ($(USEGCC)$(FC_VERSION),1)
+FC_OR_CC_VERSION := $(shell $(CC) -dumpfullversion -dumpversion 2>/dev/null | cut -d'.' -f1)
+# n.b. clang's __GNUC__ macro pretends to be gcc 4.2.1, so leave it as the empty string here if the compiler is not certain to be GCC
+endif
 BB_TRIPLET_LIBGFORTRAN_CXXABI := $(shell $(call invoke_python,$(JULIAHOME)/contrib/normalize_triplet.py) $(or $(XC_HOST),$(XC_HOST),$(BUILD_MACHINE)) "$(FC_OR_CC_VERSION)" "$(or $(shell echo '\#include <string>' | $(CXX) $(CXXFLAGS) -x c++ -dM -E - | grep _GLIBCXX_USE_CXX11_ABI | awk '{ print $$3 }' ),1)")
 BB_TRIPLET_LIBGFORTRAN := $(subst $(SPACE),-,$(filter-out cxx%,$(subst -,$(SPACE),$(BB_TRIPLET_LIBGFORTRAN_CXXABI))))
 BB_TRIPLET_CXXABI := $(subst $(SPACE),-,$(filter-out libgfortran%,$(subst -,$(SPACE),$(BB_TRIPLET_LIBGFORTRAN_CXXABI))))

contrib/normalize_triplet.py

@@ -113,9 +113,16 @@ def p(x):
         if not sys.argv[2]:
             libgfortran_version = "libgfortran5"
         else:
-            # Take the last thing that looks like a version number, and extract its major component
-            version_numbers = list(filter(lambda x: re.match("\d+\.\d+(\.\d+)?", x), sys.argv[2].split()))
-            major_ver = int(version_numbers[-1].split('.')[0])
+            # Grab the first number in the last word with a number
+            # This will be the major version number.
+            major_ver = -1
+            words = sys.argv[2].split()
+            for word in words[::-1]:
+                major_ver = re.search("[0-9]+", word)
+                if major_ver:
+                    major_ver = int(major_ver.group())
+                    break
+
             if major_ver <= 6:
                 libgfortran_version = "libgfortran3"
             elif major_ver <= 7: